diff --git a/src/Debug.h b/src/Debug.h
index 06bc483b98..a2e7da266d 100644
--- a/src/Debug.h
+++ b/src/Debug.h
@@ -137,7 +137,7 @@ public:
 
 protected:
 	Location loc;
-	Stmt* stmt;
+	Stmt* stmt = nullptr;
 	};
 
 extern bool g_policy_debug; // enable debugging facility
diff --git a/src/File.h b/src/File.h
index e5c2dab9c8..98b722228d 100644
--- a/src/File.h
+++ b/src/File.h
@@ -108,17 +108,17 @@ protected:
 	// Raises a file_opened event.
 	void RaiseOpenEvent();
 
-	FILE* f;
+	FILE* f = nullptr;
 	TypePtr t;
-	char* name;
-	char* access;
-	detail::Attributes* attrs;
-	double open_time;
-	bool is_open; // whether the file is open in a general sense
-	bool buffered;
-	bool raw_output;
+	char* name = nullptr;
+	char* access = nullptr;
+	detail::Attributes* attrs = nullptr;
+	double open_time = 0.0;
+	bool is_open = false; // whether the file is open in a general sense
+	bool buffered = false;
+	bool raw_output = false;
 
-	static const int MIN_BUFFER_SIZE = 1024;
+	static constexpr int MIN_BUFFER_SIZE = 1024;
 
 private:
 	static std::list<std::pair<std::string, File*>> open_files;
diff --git a/src/Hash.h b/src/Hash.h
index 985c71446a..615eefd466 100644
--- a/src/Hash.h
+++ b/src/Hash.h
@@ -232,7 +232,7 @@ constexpr int NUM_HASH_KEYS = HASH_KEY_STRING + 1;
 class HashKey
 	{
 public:
-	explicit HashKey() { }
+	explicit HashKey() { key_u.u32 = 0; }
 	explicit HashKey(bool b);
 	explicit HashKey(int i);
 	explicit HashKey(zeek_int_t bi);
diff --git a/src/RandTest.h b/src/RandTest.h
index 91812f1b81..d03b0254fc 100644
--- a/src/RandTest.h
+++ b/src/RandTest.h
@@ -32,7 +32,7 @@ private:
 	int64_t totalc; /* Total bytes counted */
 	int mp;
 	int sccfirst;
-	unsigned int monte[RT_MONTEN];
+	unsigned int monte[RT_MONTEN] = {0};
 	int64_t inmont, mcount;
 	double cexp, montex, montey, montepi, sccu0, scclast, scct1, scct2, scct3;
 	};
diff --git a/src/Type.cc b/src/Type.cc
index 18b95277b5..78a8ec1b0e 100644
--- a/src/Type.cc
+++ b/src/Type.cc
@@ -1001,7 +1001,7 @@ public:
 		R_INIT_RECORD, // field requires a new record
 		R_INIT_TABLE, // field requires a new table/set
 		R_INIT_VECTOR, // field requires a new vector
-		} init_type;
+		} init_type = R_INIT_NONE;
 
 	bool def_coerce = false; // whether coercion's required
 
diff --git a/src/Type.h b/src/Type.h
index 1c7b719ada..cbdc4a3602 100644
--- a/src/Type.h
+++ b/src/Type.h
@@ -725,12 +725,12 @@ protected:
 	std::vector<bool> managed_fields;
 
 	// Number of fields in the type.
-	int num_fields;
+	int num_fields = 0;
 
 	// Number of fields in the type when originally declared.
-	int num_orig_fields;
+	int num_orig_fields = 0;
 
-	type_decl_list* types;
+	type_decl_list* types = nullptr;
 	std::set<std::string> field_ids;
 	};
 
diff --git a/src/analyzer/protocol/dnp3/DNP3.h b/src/analyzer/protocol/dnp3/DNP3.h
index 7b46b5b739..d40600407a 100644
--- a/src/analyzer/protocol/dnp3/DNP3.h
+++ b/src/analyzer/protocol/dnp3/DNP3.h
@@ -23,13 +23,13 @@ protected:
 
 	struct Endpoint
 		{
-		u_char buffer[MAX_BUFFER_SIZE];
-		int buffer_len;
-		bool in_hdr;
-		int tpflags;
-		int pkt_length;
-		int pkt_cnt;
-		bool encountered_first_chunk;
+		u_char buffer[MAX_BUFFER_SIZE] = {0};
+		int buffer_len = 0;
+		bool in_hdr = false;
+		int tpflags = 0;
+		int pkt_length = 0;
+		int pkt_cnt = 0;
+		bool encountered_first_chunk = false;
 		};
 
 	bool ProcessData(int len, const u_char* data, bool orig);
diff --git a/src/analyzer/protocol/file/File.cc b/src/analyzer/protocol/file/File.cc
index f827d4fe79..961efc224b 100644
--- a/src/analyzer/protocol/file/File.cc
+++ b/src/analyzer/protocol/file/File.cc
@@ -14,7 +14,6 @@ namespace zeek::analyzer::file
 File_Analyzer::File_Analyzer(const char* name, Connection* conn)
 	: TCP_ApplicationAnalyzer(name, conn)
 	{
-	buffer_len = 0;
 	}
 
 void File_Analyzer::DeliverStream(int len, const u_char* data, bool orig)
diff --git a/src/analyzer/protocol/file/File.h b/src/analyzer/protocol/file/File.h
index c2841bf609..7cca4f7520 100644
--- a/src/analyzer/protocol/file/File.h
+++ b/src/analyzer/protocol/file/File.h
@@ -27,8 +27,8 @@ protected:
 	void Identify();
 
 	static const int BUFFER_SIZE = 1024;
-	char buffer[BUFFER_SIZE];
-	int buffer_len;
+	char buffer[BUFFER_SIZE] = {0};
+	int buffer_len = 0;
 	std::string file_id_orig;
 	std::string file_id_resp;
 	};
diff --git a/src/analyzer/protocol/rpc/RPC.h b/src/analyzer/protocol/rpc/RPC.h
index 88dcfd6c83..5b1264d813 100644
--- a/src/analyzer/protocol/rpc/RPC.h
+++ b/src/analyzer/protocol/rpc/RPC.h
@@ -99,15 +99,15 @@ protected:
 	uint32_t cred_flavor, stamp;
 	uint32_t uid, gid;
 	std::vector<int> auxgids;
-	uint32_t verf_flavor;
+	uint32_t verf_flavor = 0;
 	u_char* call_buf; // copy of original call buffer
 	std::string machinename;
 	double start_time;
 	double last_time;
-	int rpc_len; // size of the full RPC call, incl. xid and msg_type
-	int call_n; // size of call buf
-	int header_len; // size of data before the arguments
-	bool valid_call; // whether call was well-formed
+	int rpc_len = 0; // size of the full RPC call, incl. xid and msg_type
+	int call_n = 0; // size of call buf
+	int header_len = 0; // size of data before the arguments
+	bool valid_call = true; // whether call was well-formed
 
 	ValPtr v; // single (perhaps compound) value corresponding to call
 	};
diff --git a/src/input/readers/raw/Raw.h b/src/input/readers/raw/Raw.h
index 7ebb334301..a1b4e43825 100644
--- a/src/input/readers/raw/Raw.h
+++ b/src/input/readers/raw/Raw.h
@@ -78,7 +78,7 @@ private:
 
 	int64_t offset;
 
-	int pipes[6];
+	int pipes[6] = {-1};
 	pid_t childpid;
 
 	enum IoChannels
diff --git a/src/iosource/PktDumper.h b/src/iosource/PktDumper.h
index 5ad513f061..ed7689e478 100644
--- a/src/iosource/PktDumper.h
+++ b/src/iosource/PktDumper.h
@@ -99,7 +99,7 @@ protected:
 	struct Properties
 		{
 		std::string path;
-		double open_time;
+		double open_time = 0.0;
 		};
 
 	/**
diff --git a/src/logging/Manager.cc b/src/logging/Manager.cc
index 872648551e..733b62ba81 100644
--- a/src/logging/Manager.cc
+++ b/src/logging/Manager.cc
@@ -90,7 +90,7 @@ struct Manager::Stream
 
 	WriterMap writers; // Writers indexed by id/path pair.
 
-	bool enable_remote;
+	bool enable_remote = false;
 
 	~Stream();
 	};
diff --git a/src/probabilistic/CardinalityCounter.h b/src/probabilistic/CardinalityCounter.h
index 41913e1753..e3f97b7b33 100644
--- a/src/probabilistic/CardinalityCounter.h
+++ b/src/probabilistic/CardinalityCounter.h
@@ -168,7 +168,7 @@ private:
 	 * error is 1.04/sqrt(m), so the actual cardinality will be the
 	 * estimate +/- 1.04/sqrt(m) with approximately 68% probability.
 	 */
-	uint64_t m;
+	uint64_t m = 0;
 
 	/**
 	 * These are the actual buckets that are storing an estimate of the
@@ -184,9 +184,9 @@ private:
 	 * buckets that are 0 and this is used in the small error correction.
 	 * alpha_m is a multiplicative constant used in the algorithm.
 	 */
-	uint64_t V;
-	double alpha_m;
-	int p; // the log2 of m
+	uint64_t V = 0;
+	double alpha_m = 0.0;
+	int p = 0; // the log2 of m
 	};
 
 	} // namespace zeek::probabilistic::detail
diff --git a/src/probabilistic/Hasher.h b/src/probabilistic/Hasher.h
index c98b630d95..2bc47d9315 100644
--- a/src/probabilistic/Hasher.h
+++ b/src/probabilistic/Hasher.h
@@ -130,8 +130,8 @@ protected:
 	virtual HasherType Type() const = 0;
 
 private:
-	size_t k;
-	seed_t seed;
+	size_t k = 0;
+	seed_t seed = {0};
 	};
 
 /**
diff --git a/src/script_opt/ZAM/ZBody.h b/src/script_opt/ZAM/ZBody.h
index 0d3d594a8c..512fa56b15 100644
--- a/src/script_opt/ZAM/ZBody.h
+++ b/src/script_opt/ZAM/ZBody.h
@@ -73,7 +73,7 @@ private:
 	const char* func_name = nullptr;
 
 	const ZInst* insts = nullptr;
-	unsigned int ninst;
+	unsigned int ninst = 0;
 
 	FrameReMap frame_denizens;
 	int frame_size;