diff --git a/CHANGES b/CHANGES
index 343ee002ea..34cc68dd0f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,4 +1,8 @@
 
+3.1.0-dev.237 | 2019-10-31 06:37:23 +0100
+
+  * Remove "using namespace std" from header files (Jon Siwek, Corelight)
+
 3.1.0-dev.235 | 2019-10-30 15:04:13 -0700
 
   * GH-649: define missing DLT_NFLOG to support OpenBSD (Jon Siwek, Corelight)
diff --git a/VERSION b/VERSION
index 6c9ffac794..1c6a28b7f9 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-3.1.0-dev.235
+3.1.0-dev.237
diff --git a/src/Anon.h b/src/Anon.h
index 3f19cbd801..f7cbaa24f3 100644
--- a/src/Anon.h
+++ b/src/Anon.h
@@ -13,7 +13,6 @@
 #include <vector>
 #include <set>
 #include <map>
-using namespace std;
 
 #include "Reporter.h"
 #include "net_util.h"
diff --git a/src/BroString.h b/src/BroString.h
index 35102a7209..f8bcbbc7dd 100644
--- a/src/BroString.h
+++ b/src/BroString.h
@@ -7,7 +7,6 @@
 #include <iostream>
 #include <stdlib.h>
 #include <sys/types.h>
-using namespace std;
 
 #include "util.h"
 
@@ -20,23 +19,23 @@ class VectorVal;
 
 class BroString {
 public:
-	typedef vector<BroString*> Vec;
+	typedef std::vector<BroString*> Vec;
 	typedef Vec::iterator VecIt;
 	typedef Vec::const_iterator VecCIt;
 
-	typedef vector<const BroString*> CVec;
+	typedef std::vector<const BroString*> CVec;
 	typedef Vec::iterator CVecIt;
 	typedef Vec::const_iterator CVecCIt;
 
 	// IdxVecs are vectors of indices of characters in a string.
-	typedef vector<int> IdxVec;
+	typedef std::vector<int> IdxVec;
 	typedef IdxVec::iterator IdxVecIt;
 	typedef IdxVec::const_iterator IdxVecCIt;
 
 	// Constructors creating internal copies of the data passed in.
 	BroString(const u_char* str, int arg_n, int add_NUL);
 	explicit BroString(const char* str);
-	explicit BroString(const string& str);
+	explicit BroString(const std::string& str);
 	BroString(const BroString& bs);
 
 	// Constructor that takes owernship of the vector passed in.
@@ -64,7 +63,7 @@ public:
 	//
 	void Set(const u_char* str, int len, int add_NUL=1);
 	void Set(const char* str);
-	void Set(const string& str);
+	void Set(const std::string& str);
 	void Set(const BroString &str);
 
 	void SetUseFreeToDelete(int use_it)
@@ -103,13 +102,13 @@ public:
 	// Also more useful for debugging purposes since no deallocation
 	// is required on your part here.
 	//
-	ostream& Render(ostream& os, int format = ESC_SER) const;
+	std::ostream& Render(std::ostream& os, int format = ESC_SER) const;
 
 	// Reads a string from an input stream.  Unless you use a render
 	// style combination that uses ESC_SER, note that the streams
 	// will consider whitespace as a field delimiter.
 	//
-	istream& Read(istream& is, int format = ESC_SER);
+	std::istream& Read(std::istream& is, int format = ESC_SER);
 
 	// XXX Fix redundancy: strings.bif implements both to_lower
 	// XXX and to_upper; the latter doesn't use BroString::ToUpper().
@@ -165,7 +164,7 @@ public:
 };
 
 // Default output stream operator, using rendering mode EXPANDED_STRING.
-ostream& operator<<(ostream& os, const BroString& bs);
+std::ostream& operator<<(std::ostream& os, const BroString& bs);
 
 extern int Bstr_eq(const BroString* s1, const BroString* s2);
 extern int Bstr_cmp(const BroString* s1, const BroString* s2);
diff --git a/src/DFA.h b/src/DFA.h
index 12620568ae..a3b79920f6 100644
--- a/src/DFA.h
+++ b/src/DFA.h
@@ -4,6 +4,7 @@
 #pragma once
 
 #include <assert.h>
+#include <string>
 
 class DFA_State;
 
@@ -66,7 +67,7 @@ protected:
 	static unsigned int transition_counter;	// see Xtion()
 };
 
-using DigestStr = basic_string<u_char>;
+using DigestStr = std::basic_string<u_char>;
 
 class DFA_State_Cache {
 public:
diff --git a/src/Debug.h b/src/Debug.h
index a036dd264e..42fd3bd42a 100644
--- a/src/Debug.h
+++ b/src/Debug.h
@@ -5,8 +5,6 @@
 #include <vector>
 #include <map>
 #include <string>
-using namespace std;
-
 
 class Stmt;
 
@@ -35,10 +33,10 @@ class DbgWatch;
 class DbgDisplay;
 class StmtHashFn;
 
-typedef map<int, DbgBreakpoint*> BPIDMapType;
-typedef multimap<const Stmt*, DbgBreakpoint*> BPMapType;
+typedef std::map<int, DbgBreakpoint*> BPIDMapType;
+typedef std::multimap<const Stmt*, DbgBreakpoint*> BPMapType;
 
-extern string current_module;
+extern std::string current_module;
 
 class TraceState {
 public:
@@ -88,8 +86,8 @@ public:
 	Location last_loc;	// used by 'list'; the last location listed
 
 	BPIDMapType breakpoints;	// BPID -> Breakpoint
-	vector<DbgWatch*> watches;
-	vector<DbgDisplay*> displays;
+	std::vector<DbgWatch*> watches;
+	std::vector<DbgDisplay*> displays;
 	BPMapType breakpoint_map;	// maps Stmt -> Breakpoints on it
 
 protected:
@@ -135,7 +133,7 @@ extern DebuggerState g_debugger_state;
 // Multiple results can be returned depending on the input, but always
 // at least 1.
 
-vector<ParseLocationRec> parse_location_string(const string& s);
+std::vector<ParseLocationRec> parse_location_string(const std::string& s);
 
 // ### TODO: Add a bunch of hook functions for various events
 //   e.g. variable changed, breakpoint hit, etc.
@@ -171,11 +169,11 @@ Val* dbg_eval_expr(const char* expr);
 int dbg_read_internal_state();
 
 // Get line that looks like "In FnFoo(arg = val) at File:Line".
-string get_context_description(const Stmt* stmt, const Frame* frame);
+std::string get_context_description(const Stmt* stmt, const Frame* frame);
 
 extern Frame* g_dbg_locals;	// variables created within debugger context
 
-extern std::map<string, Filemap*> g_dbgfilemaps; // filename => filemap
+extern std::map<std::string, Filemap*> g_dbgfilemaps; // filename => filemap
 
 // Perhaps add a code/priority argument to do selective output.
 int debug_msg(const char* fmt, ...) __attribute__ ((format (printf, 1, 2)));
diff --git a/src/DebugCmds.h b/src/DebugCmds.h
index 7eb0f025a7..470e4ae993 100644
--- a/src/DebugCmds.h
+++ b/src/DebugCmds.h
@@ -6,7 +6,6 @@
 #include <stdlib.h>
 #include <string>
 #include <vector>
-using namespace std;
 
 #include "Queue.h"
 #include "DebugCmdConstants.h"
@@ -23,7 +22,7 @@ public:
 
 	int Cmd() const		{ return cmd; }
 	int NumNames() const	{ return num_names; }
-	const vector<const char *>& Names() const	{ return names; }
+	const std::vector<const char *>& Names() const	{ return names; }
 	bool ResumeExecution() const	{ return resume_execution; }
 	const char* Helpstring() const	{ return helpstring; }
 	bool Repeatable() const	{ return repeatable; }
@@ -32,7 +31,7 @@ protected:
 	DebugCmd cmd;
 
 	int num_names;
-	vector<const char*> names;
+	std::vector<const char*> names;
 
 	// Whether executing this should restart execution of the script.
 	bool resume_execution;
@@ -57,14 +56,14 @@ const DebugCmdInfo* get_debug_cmd_info(DebugCmd cmd);
 // on whether or not the prefix supplied matches a name (DebugCmdString)
 // of the corresponding DebugCmd. The size of the array should be at
 // least NUM_DEBUG_CMDS. The total number of matches is returned.
-int find_all_matching_cmds(const string& prefix, const char* array_of_matches[]);
+int find_all_matching_cmds(const std::string& prefix, const char* array_of_matches[]);
 
 // Implementation of debugging commands.
 //
 // These functions return <= 0 if failure, > 0 for success.
 // More particular return values are command-specific: see comments w/function.
 
-typedef int DbgCmdFn(DebugCmd cmd, const vector<string>& args);
+typedef int DbgCmdFn(DebugCmd cmd, const std::vector<std::string>& args);
 
 DbgCmdFn dbg_cmd_backtrace;
 DbgCmdFn dbg_cmd_frame;
diff --git a/src/Desc.h b/src/Desc.h
index fadf61eac7..ff59aba43c 100644
--- a/src/Desc.h
+++ b/src/Desc.h
@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <set>
 #include <utility>
+#include <string>
 
 #include "BroString.h"
 
@@ -56,13 +57,13 @@ public:
 	void EnableUTF8();
 	void AddEscapeSequence(const char* s) { escape_sequences.insert(s); }
 	void AddEscapeSequence(const char* s, size_t n)
-	    { escape_sequences.insert(string(s, n)); }
-	void AddEscapeSequence(const string & s)
+	    { escape_sequences.insert(std::string(s, n)); }
+	void AddEscapeSequence(const std::string & s)
 	    { escape_sequences.insert(s); }
 	void RemoveEscapeSequence(const char* s) { escape_sequences.erase(s); }
 	void RemoveEscapeSequence(const char* s, size_t n)
-	    { escape_sequences.erase(string(s, n)); }
-	void RemoveEscapeSequence(const string & s)
+	    { escape_sequences.erase(std::string(s, n)); }
+	void RemoveEscapeSequence(const std::string & s)
 	    { escape_sequences.erase(s); }
 
 	void PushIndent();
@@ -76,7 +77,7 @@ public:
 
 	void Add(const char* s, int do_indent=1);
 	void AddN(const char* s, int len)	{ AddBytes(s, len); }
-	void Add(const string& s)	{ AddBytes(s.data(), s.size()); }
+	void Add(const std::string& s)	{ AddBytes(s.data(), s.size()); }
 	void Add(int i);
 	void Add(uint32_t u);
 	void Add(int64_t i);
@@ -119,7 +120,7 @@ public:
 
 	// Bypasses the escaping enabled via SetEscape().
 	void AddRaw(const char* s, int len)	{ AddBytesRaw(s, len); }
-	void AddRaw(const string &s)		{ AddBytesRaw(s.data(), s.size()); }
+	void AddRaw(const std::string &s)		{ AddBytesRaw(s.data(), s.size()); }
 
 	// Returns the description as a string.
 	const char* Description() const		{ return (const char*) base; }
@@ -167,7 +168,7 @@ protected:
 	 *         second element.  The first element may be 0 if nothing is
 	 *         to be escaped.
 	 */
-	pair<const char*, size_t> FirstEscapeLoc(const char* bytes, size_t n);
+	std::pair<const char*, size_t> FirstEscapeLoc(const char* bytes, size_t n);
 
 	/**
 	 * @param start start of string to check for starting with an espace
@@ -187,7 +188,7 @@ protected:
 
 	bool utf8; // whether valid utf-8 sequences may pass through unescaped
 	bool escape;	// escape unprintable characters in output?
-	typedef set<string> escape_set;
+	typedef std::set<std::string> escape_set;
 	escape_set escape_sequences; // additional sequences of chars to escape
 
 	BroFile* f;	// or the file we're using.
diff --git a/src/ID.h b/src/ID.h
index 4ebcc9769d..b3e36ebd4f 100644
--- a/src/ID.h
+++ b/src/ID.h
@@ -27,7 +27,7 @@ public:
 	bool IsExport() const           { return is_export; }
 	void SetExport()                { is_export = true; }
 
-	string ModuleName() const;
+	std::string ModuleName() const;
 
 	void SetType(BroType* t)	{ Unref(type); type = t; }
 	BroType* Type()			{ return type; }
@@ -83,7 +83,7 @@ public:
 
 	void MakeDeprecated(Expr* deprecation);
 
-	string GetDeprecationWarning() const;
+	std::string GetDeprecationWarning() const;
 
 	void Error(const char* msg, const BroObj* o2 = 0);
 
@@ -106,7 +106,7 @@ public:
 
 	// Takes ownership of callback.
 	void AddOptionHandler(Func* callback, int priority);
-	vector<Func*> GetOptionHandlers() const;
+	std::vector<Func*> GetOptionHandlers() const;
 
 protected:
 	ID()	{ name = 0; type = 0; val = 0; attrs = 0; }
diff --git a/src/PacketDumper.h b/src/PacketDumper.h
index e45adeb41f..78469b3d7c 100644
--- a/src/PacketDumper.h
+++ b/src/PacketDumper.h
@@ -2,8 +2,6 @@
 
 #pragma once
 
-using namespace std;
-
 #include <queue>
 #include <set>
 
@@ -35,5 +33,5 @@ struct ltipid {
 		}
 };
 
-typedef set<IP_ID, ltipid> IP_IDSet;
+typedef std::set<IP_ID, ltipid> IP_IDSet;
 uint16_t NextIP_ID(const uint32_t src_addr, const uint16_t id);
diff --git a/src/RE.h b/src/RE.h
index 17fa36c0cf..ace38f2767 100644
--- a/src/RE.h
+++ b/src/RE.h
@@ -10,6 +10,7 @@
 
 #include <set>
 #include <map>
+#include <string>
 
 #include <ctype.h>
 typedef int (*cce_func)(int);
@@ -60,7 +61,7 @@ public:
 	// functionality.
 	std::string LookupDef(const std::string& def);
 
-	void InsertCCL(const char* txt, CCL* ccl) { ccl_dict[string(txt)] = ccl; }
+	void InsertCCL(const char* txt, CCL* ccl) { ccl_dict[std::string(txt)] = ccl; }
 	int InsertCCL(CCL* ccl)
 		{
 		ccl_list.push_back(ccl);
@@ -68,7 +69,7 @@ public:
 		}
 	CCL* LookupCCL(const char* txt)
 		{
-		const auto& iter = ccl_dict.find(string(txt));
+		const auto& iter = ccl_dict.find(std::string(txt));
 		if ( iter != ccl_dict.end() )
 			return iter->second;
 
@@ -125,8 +126,8 @@ protected:
 	int multiline;
 	char* pattern_text;
 
-	std::map<string, string> defs;
-	std::map<string, CCL*> ccl_dict;
+	std::map<std::string, std::string> defs;
+	std::map<std::string, CCL*> ccl_dict;
 	PList<CCL> ccl_list;
 	EquivClass equiv_class;
 	int* ecs;
diff --git a/src/Rule.h b/src/Rule.h
index bc478f18f3..663174f28f 100644
--- a/src/Rule.h
+++ b/src/Rule.h
@@ -15,7 +15,7 @@ class RuleHdrTest;
 class Rule;
 
 typedef PList<Rule> rule_list;
-typedef std::map<string, Rule*> rule_dict;
+typedef std::map<std::string, Rule*> rule_dict;
 
 class Rule {
 public:
diff --git a/src/Scope.h b/src/Scope.h
index 2c25863e23..9b046fafa1 100644
--- a/src/Scope.h
+++ b/src/Scope.h
@@ -47,7 +47,7 @@ public:
 	BroType* ReturnType() const	{ return return_type; }
 
 	size_t Length() const		{ return local.size(); }
-	std::map<string, ID*>& Vars()	{ return local; }
+	std::map<std::string, ID*>& Vars()	{ return local; }
 
 	ID* GenerateTemporary(const char* name);
 
@@ -66,7 +66,7 @@ protected:
 	ID* scope_id;
 	attr_list* attrs;
 	BroType* return_type;
-	std::map<string, ID*> local;
+	std::map<std::string, ID*> local;
 	id_list* inits;
 };
 
@@ -90,4 +90,4 @@ extern Scope* current_scope();
 extern Scope* global_scope();
 
 // Current module (identified by its name).
-extern string current_module;
+extern std::string current_module;
diff --git a/src/SerializationFormat.h b/src/SerializationFormat.h
index 03bf758c31..772837ed91 100644
--- a/src/SerializationFormat.h
+++ b/src/SerializationFormat.h
@@ -4,8 +4,6 @@
 
 #include <string>
 
-using namespace std;
-
 #include "util.h"
 
 class IPAddr;
@@ -29,7 +27,7 @@ public:
 	virtual bool Read(char* v, const char* tag) = 0;
 	virtual bool Read(bool* v, const char* tag) = 0;
 	virtual bool Read(double* d, const char* tag) = 0;
-	virtual bool Read(string* s, const char* tag) = 0;
+	virtual bool Read(std::string* s, const char* tag) = 0;
 	virtual bool Read(IPAddr* addr, const char* tag) = 0;
 	virtual bool Read(IPPrefix* prefix, const char* tag) = 0;
 	virtual bool Read(struct in_addr* addr, const char* tag) = 0;
@@ -63,7 +61,7 @@ public:
 	virtual bool Write(double d, const char* tag) = 0;
 	virtual bool Write(const char* s, const char* tag) = 0;
 	virtual bool Write(const char* buf, int len, const char* tag) = 0;
-	virtual bool Write(const string& s, const char* tag) = 0;
+	virtual bool Write(const std::string& s, const char* tag) = 0;
 	virtual bool Write(const IPAddr& addr, const char* tag) = 0;
 	virtual bool Write(const IPPrefix& prefix, const char* tag) = 0;
 	virtual bool Write(const struct in_addr& addr, const char* tag) = 0;
@@ -108,7 +106,7 @@ public:
 	bool Read(bool* v, const char* tag) override;
 	bool Read(double* d, const char* tag) override;
 	bool Read(char** str, int* len, const char* tag) override;
-	bool Read(string* s, const char* tag) override;
+	bool Read(std::string* s, const char* tag) override;
 	bool Read(IPAddr* addr, const char* tag) override;
 	bool Read(IPPrefix* prefix, const char* tag) override;
 	bool Read(struct in_addr* addr, const char* tag) override;
@@ -123,7 +121,7 @@ public:
 	bool Write(double d, const char* tag) override;
 	bool Write(const char* s, const char* tag) override;
 	bool Write(const char* buf, int len, const char* tag) override;
-	bool Write(const string& s, const char* tag) override;
+	bool Write(const std::string& s, const char* tag) override;
 	bool Write(const IPAddr& addr, const char* tag) override;
 	bool Write(const IPPrefix& prefix, const char* tag) override;
 	bool Write(const struct in_addr& addr, const char* tag) override;
diff --git a/src/SmithWaterman.h b/src/SmithWaterman.h
index 541f777b89..3d29eb15a3 100644
--- a/src/SmithWaterman.h
+++ b/src/SmithWaterman.h
@@ -4,7 +4,6 @@
 
 #include "BroString.h"
 #include <map>
-using namespace std;
 
 // BroSubstrings are essentially BroStrings, augmented with indexing
 // information required for the Smith-Waterman algorithm.  Each substring
@@ -15,7 +14,7 @@ using namespace std;
 class BroSubstring : public BroString {
 
 public:
-	typedef vector<BroSubstring*> Vec;
+	typedef std::vector<BroSubstring*> Vec;
 	typedef Vec::iterator VecIt;
 	typedef Vec::const_iterator VecCIt;
 
@@ -36,11 +35,11 @@ public:
 		int index;
 	};
 
-	typedef vector<BSSAlign> BSSAlignVec;
+	typedef std::vector<BSSAlign> BSSAlignVec;
 	typedef BSSAlignVec::iterator BSSAlignVecIt;
 	typedef BSSAlignVec::const_iterator BSSAlignVecCIt;
 
-	explicit BroSubstring(const string& string)
+	explicit BroSubstring(const std::string& string)
 		: BroString(string), _num(), _new(false) { }
 
 	explicit BroSubstring(const BroString& string)
@@ -76,7 +75,7 @@ public:
 						unsigned int index);
 
 private:
-	typedef map<string, void*> DataMap;
+	typedef std::map<std::string, void*> DataMap;
 	typedef DataMap::iterator DataMapIt;
 
 	BroSubstring();
diff --git a/src/Type.h b/src/Type.h
index 04c2bfac47..a4261e453a 100644
--- a/src/Type.h
+++ b/src/Type.h
@@ -262,8 +262,8 @@ public:
 
 	virtual unsigned MemoryAllocation() const;
 
-	void SetName(const string& arg_name) { name = arg_name; }
-	const string& GetName() const { return name; }
+	void SetName(const std::string& arg_name) { name = arg_name; }
+	const std::string& GetName() const { return name; }
 
 	typedef std::map<std::string, std::set<BroType*> > TypeAliasMap;
 
@@ -283,7 +283,7 @@ private:
 	InternalTypeTag internal_tag;
 	bool is_network_order;
 	bool base_type;
-	string name;
+	std::string name;
 
 	static TypeAliasMap type_aliases;
 };
@@ -402,7 +402,7 @@ public:
 	const BroType* YieldType() const override;
 	void SetYieldType(BroType* arg_yield)	{ yield = arg_yield; }
 	function_flavor Flavor() const { return flavor; }
-	string FlavorString() const;
+	std::string FlavorString() const;
 
 	// Used to convert a function type to an event or hook type.
 	void ClearYieldType(function_flavor arg_flav)
@@ -504,7 +504,7 @@ public:
 		return decl && decl->FindAttr(at) != 0;
 		}
 
-	string GetFieldDeprecationWarning(int field, bool has_check) const;
+	std::string GetFieldDeprecationWarning(int field, bool has_check) const;
 
 protected:
 	RecordType() { types = 0; }
@@ -537,11 +537,11 @@ protected:
 
 class OpaqueType : public BroType {
 public:
-	explicit OpaqueType(const string& name);
+	explicit OpaqueType(const std::string& name);
 	OpaqueType* ShallowClone() override { return new OpaqueType(name); }
 	~OpaqueType() override { };
 
-	const string& Name() const { return name; }
+	const std::string& Name() const { return name; }
 
 	void Describe(ODesc* d) const override;
 	void DescribeReST(ODesc* d, bool roles_only = false) const override;
@@ -549,29 +549,29 @@ public:
 protected:
 	OpaqueType() { }
 
-	string name;
+	std::string name;
 };
 
 class EnumType : public BroType {
 public:
-	typedef std::list<std::pair<string, bro_int_t> > enum_name_list;
+	typedef std::list<std::pair<std::string, bro_int_t> > enum_name_list;
 
 	explicit EnumType(const EnumType* e);
-	explicit EnumType(const string& arg_name);
+	explicit EnumType(const std::string& arg_name);
 	EnumType* ShallowClone() override;
 	~EnumType() override;
 
 	// The value of this name is next internal counter value, starting
 	// with zero. The internal counter is incremented.
-	void AddName(const string& module_name, const char* name, bool is_export, Expr* deprecation = nullptr);
+	void AddName(const std::string& module_name, const char* name, bool is_export, Expr* deprecation = nullptr);
 
 	// The value of this name is set to val. Once a value has been
 	// explicitly assigned using this method, no further names can be
 	// added that aren't likewise explicitly initalized.
-	void AddName(const string& module_name, const char* name, bro_int_t val, bool is_export, Expr* deprecation = nullptr);
+	void AddName(const std::string& module_name, const char* name, bro_int_t val, bool is_export, Expr* deprecation = nullptr);
 
 	// -1 indicates not found.
-	bro_int_t Lookup(const string& module_name, const char* name) const;
+	bro_int_t Lookup(const std::string& module_name, const char* name) const;
 	const char* Lookup(bro_int_t value) const; // Returns 0 if not found
 
 	// Returns the list of defined names with their values. The names
@@ -585,10 +585,10 @@ public:
 protected:
 	EnumType() { counter = 0; }
 
-	void AddNameInternal(const string& module_name,
+	void AddNameInternal(const std::string& module_name,
 			const char* name, bro_int_t val, bool is_export);
 
-	void CheckAndAddName(const string& module_name,
+	void CheckAndAddName(const std::string& module_name,
 	                     const char* name, bro_int_t val, bool is_export,
 	                     Expr* deprecation = nullptr);
 
diff --git a/src/input.h b/src/input.h
index be898d154b..327423ed9c 100644
--- a/src/input.h
+++ b/src/input.h
@@ -4,7 +4,6 @@
 
 #include <vector>
 #include <string>
-using namespace std;
 
 #include "BroList.h"
 
@@ -40,7 +39,7 @@ extern const char* prog;
 
 extern name_list prefixes;	// -p flag
 extern char* command_line_policy;	// -e flag
-extern vector<string> params;
+extern std::vector<std::string> params;
 
 class Stmt;
 extern Stmt* stmts;	// global statements
diff --git a/src/module_util.cc b/src/module_util.cc
index d5817a7d7a..500d7f4d08 100644
--- a/src/module_util.cc
+++ b/src/module_util.cc
@@ -5,6 +5,8 @@
 #include <string.h>
 #include "module_util.h"
 
+using namespace std;
+
 static int streq(const char* s1, const char* s2)
 	{
 	return ! strcmp(s1, s2);
diff --git a/src/module_util.h b/src/module_util.h
index 4e865380d2..5e1597a987 100644
--- a/src/module_util.h
+++ b/src/module_util.h
@@ -6,14 +6,12 @@
 
 #include <string>
 
-using namespace std;
-
 static const char* GLOBAL_MODULE_NAME = "GLOBAL";
 
-extern string extract_module_name(const char* name);
-extern string extract_var_name(const char* name);
-extern string normalized_module_name(const char* module_name); // w/o ::
+extern std::string extract_module_name(const char* name);
+extern std::string extract_var_name(const char* name);
+extern std::string normalized_module_name(const char* module_name); // w/o ::
 
 // Concatenates module_name::var_name unless var_name is already fully
 // qualified, in which case it is returned unmodified.
-extern string make_full_var_name(const char* module_name, const char* var_name);
+extern std::string make_full_var_name(const char* module_name, const char* var_name);
diff --git a/src/probabilistic/BloomFilter.h b/src/probabilistic/BloomFilter.h
index 629605c6b6..950235e5f5 100644
--- a/src/probabilistic/BloomFilter.h
+++ b/src/probabilistic/BloomFilter.h
@@ -3,6 +3,7 @@
 #pragma once
 
 #include <vector>
+#include <string>
 
 #include <broker/data.hh>
 #include <broker/expected.hh>
@@ -75,7 +76,7 @@ public:
 	 * Returns a string with a representation of the Bloom filter's
 	 * internal state. This is for debugging/testing purposes only.
 	 */
-	virtual string InternalState() const = 0;
+	virtual std::string InternalState() const = 0;
 
 	broker::expected<broker::data> Serialize() const;
 	static std::unique_ptr<BloomFilter> Unserialize(const broker::data& data);
@@ -154,7 +155,7 @@ public:
 	void Clear() override;
 	bool Merge(const BloomFilter* other) override;
 	BasicBloomFilter* Clone() const override;
-	string InternalState() const override;
+	std::string InternalState() const override;
 
 protected:
 	friend class BloomFilter;
@@ -203,7 +204,7 @@ public:
 	void Clear() override;
 	bool Merge(const BloomFilter* other) override;
 	CountingBloomFilter* Clone() const override;
-	string InternalState() const override;
+	std::string InternalState() const override;
 
 protected:
 	friend class BloomFilter;