diff --git a/src/Debug.h b/src/Debug.h
index a83e05c224..89884cfb0b 100644
--- a/src/Debug.h
+++ b/src/Debug.h
@@ -54,7 +54,7 @@ public:
 	void TraceOn();
 	void TraceOff();
 
-	int LogTrace(const char* fmt, ...);
+	int LogTrace(const char* fmt, ...) __attribute__((format(printf, 2, 3)));;
 
 protected:
 	bool dbgtrace;		// print an execution trace
diff --git a/src/Reporter.cc b/src/Reporter.cc
index e5a37bf13b..cbd8402c9d 100644
--- a/src/Reporter.cc
+++ b/src/Reporter.cc
@@ -221,7 +221,7 @@ void Reporter::WeirdFlowHelper(const IPAddr& orig, const IPAddr& resp, const cha
 
 void Reporter::Weird(const char* name)
 	{
-	WeirdHelper(net_weird, 0, 0, name);
+	WeirdHelper(net_weird, 0, 0, "%s", name);
 	}
 
 void Reporter::Weird(Connection* conn, const char* name, const char* addl)
diff --git a/src/Reporter.h b/src/Reporter.h
index b9ba4f1b95..19cdbb7e82 100644
--- a/src/Reporter.h
+++ b/src/Reporter.h
@@ -93,7 +93,7 @@ public:
 
 	// Report an analyzer error. That analyzer will be set to not process
 	// any further input, but Bro otherwise continues normally.
-	void AnalyzerError(analyzer::Analyzer* a, const char* fmt, ...);
+	void AnalyzerError(analyzer::Analyzer* a, const char* fmt, ...) __attribute__((format(printf, 3, 4)));;
 
 	// Toggle whether non-fatal messages should be reported through the
 	// scripting layer rather on standard output. Fatal errors are always
@@ -127,8 +127,8 @@ private:
 
 	// The order if addl, name needs to be like that since fmt_name can
 	// contain format specifiers
-	void WeirdHelper(EventHandlerPtr event, Val* conn_val, const char* addl, const char* fmt_name, ...);
-	void WeirdFlowHelper(const IPAddr& orig, const IPAddr& resp, const char* fmt_name, ...);
+	void WeirdHelper(EventHandlerPtr event, Val* conn_val, const char* addl, const char* fmt_name, ...) __attribute__((format(printf, 5, 6)));;
+	void WeirdFlowHelper(const IPAddr& orig, const IPAddr& resp, const char* fmt_name, ...) __attribute__((format(printf, 4, 5)));;
 
 	int errors;
 	bool via_events;
diff --git a/src/input/readers/raw/Raw.cc b/src/input/readers/raw/Raw.cc
index 843d1d25d1..cfa7b72602 100644
--- a/src/input/readers/raw/Raw.cc
+++ b/src/input/readers/raw/Raw.cc
@@ -526,7 +526,7 @@ void Raw::WriteToStdin()
 
 	if ( errno != 0 && errno != EAGAIN && errno != EWOULDBLOCK )
 		{
-		Error(Fmt("Writing to child process stdin failed: %d. Stopping writing at position %d", errno, pos));
+		Error(Fmt("Writing to child process stdin failed: %d. Stopping writing at position %" PRIu64, errno, pos));
 		stdin_towrite = 0;
 		}
 
diff --git a/src/input/readers/sqlite/SQLite.cc b/src/input/readers/sqlite/SQLite.cc
index 47e8cc3ed7..c970e60182 100644
--- a/src/input/readers/sqlite/SQLite.cc
+++ b/src/input/readers/sqlite/SQLite.cc
@@ -94,7 +94,7 @@ bool SQLite::DoInit(const ReaderInfo& info, int arg_num_fields, const threading:
 	ReaderInfo::config_map::const_iterator it = info.config.find("query");
 	if ( it == info.config.end() )
 		{
-		Error(Fmt("No query specified when setting up SQLite data source. Aborting.", info.source));
+		Error(Fmt("No query specified when setting up SQLite data source %s. Aborting.", info.source));
 		return false;
 		}
 	else
diff --git a/src/logging/writers/sqlite/SQLite.cc b/src/logging/writers/sqlite/SQLite.cc
index f7b85889f3..977a0c6089 100644
--- a/src/logging/writers/sqlite/SQLite.cc
+++ b/src/logging/writers/sqlite/SQLite.cc
@@ -174,7 +174,7 @@ bool SQLite::DoInit(const WriterInfo& info, int arg_num_fields,
 		string type = GetTableType(field->type, field->subtype);
 		if ( type == "" )
 			{
-			InternalError(Fmt("Could not determine type for field %lu:%s", i, fieldname));
+			InternalError(Fmt("Could not determine type for field %u:%s", i, fieldname));
 			return false;
 			}
 
diff --git a/src/threading/BasicThread.h b/src/threading/BasicThread.h
index 117506c418..6386e5ae66 100644
--- a/src/threading/BasicThread.h
+++ b/src/threading/BasicThread.h
@@ -116,7 +116,7 @@ public:
 	 * This is safe to call from Run() but must not be used from any
 	 * other thread than the current one.
 	 */
-	const char* Fmt(const char* format, ...);
+	const char* Fmt(const char* format, ...)  __attribute__((format(printf, 2, 3)));;
 
 	/**
 	 * A version of strerror() that the thread can safely use. This is