diff --git a/aux/broccoli b/aux/broccoli
index 31c3d1d9ef..aff2b1eba1 160000
--- a/aux/broccoli
+++ b/aux/broccoli
@@ -1 +1 @@
-Subproject commit 31c3d1d9efa706969f0cd98223444c5f064a6fa7
+Subproject commit aff2b1eba11d9df4e580ec0a039e01c94bb9c6a2
diff --git a/src/CompHash.cc b/src/CompHash.cc
index fcd5f61e53..6893cafd8f 100644
--- a/src/CompHash.cc
+++ b/src/CompHash.cc
@@ -644,7 +644,7 @@ const char* CompositeHash::RecoverOneVal(const HashKey* k, const char* kp0,
 			Func* f = Func::GetFuncPtrByID(*kp);
 
 			if ( ! f )
-				reporter->InternalError("failed to look up unique function id %"PRIu32" in CompositeHash::RecoverOneVal()");
+				reporter->InternalError("failed to look up unique function id %" PRIu32 " in CompositeHash::RecoverOneVal()", *kp);
 
 			pval = new Val(f);
 
diff --git a/src/File.cc b/src/File.cc
index ada75fe401..37ce7c0b4b 100644
--- a/src/File.cc
+++ b/src/File.cc
@@ -285,7 +285,7 @@ FILE* BroFile::BringIntoCache()
 
 	if ( ! f )
 		{
-		reporter->Error("can't open %s", this);
+		reporter->Error("can't open %s", name);
 
 		f = fopen("/dev/null", "w");
 
diff --git a/src/OSFinger.h b/src/OSFinger.h
index 1e745505eb..e5a0829640 100644
--- a/src/OSFinger.h
+++ b/src/OSFinger.h
@@ -103,7 +103,7 @@ protected:
 
 	void Error(const char* msg)
 		{
-		reporter->Error(msg);
+		reporter->Error("%s", msg);
 		err = true;
 		}
 
diff --git a/src/RemoteSerializer.cc b/src/RemoteSerializer.cc
index e359a4a749..6a0ac54446 100644
--- a/src/RemoteSerializer.cc
+++ b/src/RemoteSerializer.cc
@@ -3085,7 +3085,7 @@ void RemoteSerializer::FatalError(const char* msg)
 	{
 	msg = fmt("fatal error, shutting down communication: %s", msg);
 	Log(LogError, msg);
-	reporter->Error(msg);
+	reporter->Error("%s", msg);
 
 	closed = true;
 	kill(child_pid, SIGQUIT);
diff --git a/src/Reporter.h b/src/Reporter.h
index d0fc66299b..6c57a26cba 100644
--- a/src/Reporter.h
+++ b/src/Reporter.h
@@ -15,6 +15,13 @@
 class Connection;
 class Location;
 
+// Check printf-style variadic arguments if we can.
+#if __GNUC__
+#define FMT_ATTR __attribute__((format(printf, 2, 3))) // sic! 1st is "this" I guess.
+#else
+#define FMT_ATTR
+#endif
+
 class Reporter {
 public:
 	Reporter();
@@ -22,25 +29,25 @@ public:
 
 	// Report an informational message, nothing that needs specific
 	// attention.
-	void Info(const char* fmt, ...);
+	void Info(const char* fmt, ...) FMT_ATTR;
 
 	// Report a warning that may indicate a problem.
-	void Warning(const char* fmt, ...);
+	void Warning(const char* fmt, ...) FMT_ATTR;
 
 	// Report a non-fatal error. Processing proceeds normally after the error
 	// has been reported.
-	void Error(const char* fmt, ...);
+	void Error(const char* fmt, ...) FMT_ATTR;
 
 	// Returns the number of errors reported so far.
 	int Errors()	{ return errors; }
 
 	// Report a fatal error. Bro will terminate after the message has been
 	// reported.
-	void FatalError(const char* fmt, ...);
+	void FatalError(const char* fmt, ...) FMT_ATTR;
 
 	// Report a fatal error. Bro will terminate after the message has been
 	// reported and always generate a core dump.
-	void FatalErrorWithCore(const char* fmt, ...);
+	void FatalErrorWithCore(const char* fmt, ...) FMT_ATTR;
 
 	// Report a traffic weirdness, i.e., an unexpected protocol situation
 	// that may lead to incorrectly processing a connnection.
@@ -51,15 +58,15 @@ public:
 
 	// Syslog a message. This methods does nothing if we're running
 	// offline from a trace.
-	void Syslog(const char* fmt, ...);
+	void Syslog(const char* fmt, ...) FMT_ATTR;
 
 	// Report about a potential internal problem. Bro will continue
 	// normally.
-	void InternalWarning(const char* fmt, ...);
+	void InternalWarning(const char* fmt, ...) FMT_ATTR;
 
 	// Report an internal program error. Bro will terminate with a core
 	// dump after the message has been reported.
-	void InternalError(const char* fmt, ...);
+	void InternalError(const char* fmt, ...) FMT_ATTR;
 
 	// Toggle whether non-fatal messages should be reported through the
 	// scripting layer rather on standard output. Fatal errors are always
diff --git a/src/Serializer.cc b/src/Serializer.cc
index d38e8b3976..b82da0aaf3 100644
--- a/src/Serializer.cc
+++ b/src/Serializer.cc
@@ -909,7 +909,7 @@ bool FileSerializer::Read(UnserialInfo* info, const char* file, bool header)
 
 void FileSerializer::ReportError(const char* str)
 	{
-	reporter->Error(str);
+	reporter->Error("%s", str);
 	}
 
 void FileSerializer::GotID(ID* id, Val* val)
diff --git a/src/Serializer.h b/src/Serializer.h
index eabdbc62c1..db09cc837f 100644
--- a/src/Serializer.h
+++ b/src/Serializer.h
@@ -261,7 +261,7 @@ public:
 	virtual ~CloneSerializer()	{ }
 
 protected:
-	virtual void ReportError(const char* msg)	{ reporter->Error(msg); }
+	virtual void ReportError(const char* msg)	{ reporter->Error("%s", msg); }
 	virtual void GotID(ID* id, Val* val)	{ }
 	virtual void GotEvent(const char* name, double time,
 				EventHandlerPtr event, val_list* args)	{ }
diff --git a/src/Val.cc b/src/Val.cc
index 164994b3b8..9238315b49 100644
--- a/src/Val.cc
+++ b/src/Val.cc
@@ -2118,7 +2118,7 @@ Val* TableVal::Delete(const Val* index)
 	Val* va = v ? (v->Value() ? v->Value() : this->Ref()) : 0;
 
 	if ( subnets && ! subnets->Remove(index) )
-		reporter->InternalError( "index not in prefix table" );
+		reporter->InternalError("index not in prefix table");
 
 	if ( LoggingAccess() )
 		{
@@ -2160,7 +2160,7 @@ Val* TableVal::Delete(const HashKey* k)
 		{
 		Val* index = table_hash->RecoverVals(k);
 		if ( ! subnets->Remove(index) )
-			reporter->InternalError( "index not in prefix table" );
+			reporter->InternalError("index not in prefix table");
 		Unref(index);
 		}
 
@@ -2417,7 +2417,7 @@ void TableVal::DoExpire(double t)
 				{
 				Val* index = RecoverIndex(k);
 				if ( ! subnets->Remove(index) )
-					reporter->InternalError( "index not in prefix table" );
+					reporter->InternalError("index not in prefix table");
 				Unref(index);
 				}
 
diff --git a/src/bro.bif b/src/bro.bif
index d8cc9d4696..0fd20397f0 100644
--- a/src/bro.bif
+++ b/src/bro.bif
@@ -1855,7 +1855,7 @@ function decode_base64%(s: string%): string
 		return new StringVal(t);
 	else
 		{
-		reporter->Error("error in decoding string %s", @ARG@[0]);
+		reporter->Error("error in decoding string %s", s->CheckString());
 		return new StringVal("");
 		}
 	%}
@@ -1987,8 +1987,8 @@ function precompile_pcap_filter%(id: PcapFilterID, s: string%): bool
 		if ( ! pkt_srcs[i]->PrecompileFilter(id->ForceAsInt(),
 							s->CheckString()) )
 			{
-			reporter->Error( "precompile_pcap_filter: %s",
-				pkt_srcs[i]->ErrorMsg() );
+			reporter->Error("precompile_pcap_filter: %s",
+				pkt_srcs[i]->ErrorMsg());
 			success = false;
 			}
 		}
diff --git a/src/main.cc b/src/main.cc
index 678b21affb..f450537d5e 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -951,7 +951,7 @@ int main(int argc, char** argv)
 		{
 		reporter->Info("invoked event handlers:");
 		for ( int i = 0; i < alive_handlers->length(); ++i )
-			reporter->Info((*alive_handlers)[i]);
+			reporter->Info("%s", (*alive_handlers)[i]);
 		}
 
 	delete alive_handlers;
diff --git a/src/net_util.cc b/src/net_util.cc
index 233548e34e..c0bacc98b2 100644
--- a/src/net_util.cc
+++ b/src/net_util.cc
@@ -283,7 +283,7 @@ uint32 mask_addr(uint32 a, uint32 top_bits_to_keep)
 	{
 	if ( top_bits_to_keep > 32 )
 		{
-		reporter->Error("bad address mask value %s", top_bits_to_keep);
+		reporter->Error("bad address mask value %d", top_bits_to_keep);
 		return a;
 		}
 
diff --git a/src/parse.y b/src/parse.y
index 1035155963..495931aae0 100644
--- a/src/parse.y
+++ b/src/parse.y
@@ -1593,7 +1593,7 @@ resolve_id:
 			$$ = lookup_ID($1, current_module.c_str());
 
 			if ( ! $$ )
-				reporter->Error("identifier not defined:", $1);
+				reporter->Error("identifier not defined: %s", $1);
 
 			delete [] $1;
 			}
@@ -1650,7 +1650,7 @@ int yyerror(const char msg[])
 		strcat(msgbuf, "\nDocumentation mode is enabled: "
 		       "remember to check syntax of ## style comments\n");
 
-	reporter->Error(msgbuf);
+	reporter->Error("%s", msgbuf);
 
 	return 0;
 	}
diff --git a/src/scan.l b/src/scan.l
index 2b1d86929a..88d4e9e5e0 100644
--- a/src/scan.l
+++ b/src/scan.l
@@ -50,7 +50,7 @@ char last_tok[128];
 // a read fails.
 #define YY_INPUT(buf,result,max_size) \
 	if ( ((result = fread(buf, 1, max_size, yyin)) == 0) && ferror(yyin) ) \
-		reporter->Error(fmt("read failed with \"%s\"", strerror(errno)));
+		reporter->Error("read failed with \"%s\"", strerror(errno));
 
 // reST documents that we've created (or have at least opened so far).
 std::list<BroDoc*> docs_generated;
@@ -408,7 +408,7 @@ F	RET_CONST(new Val(false, TYPE_BOOL))
 		uint32 p = atoi(yytext);
 		if ( p > 65535 )
 			{
-			reporter->Error("bad port number -", yytext);
+			reporter->Error("bad port number - %s", yytext);
 			p = 0;
 			}
 		RET_CONST(new PortVal(p, TRANSPORT_TCP))
@@ -417,7 +417,7 @@ F	RET_CONST(new Val(false, TYPE_BOOL))
 		uint32 p = atoi(yytext);
 		if ( p > 65535 )
 			{
-			reporter->Error("bad port number -", yytext);
+			reporter->Error("bad port number - %s", yytext);
 			p = 0;
 			}
 		RET_CONST(new PortVal(p, TRANSPORT_UDP))
@@ -426,7 +426,7 @@ F	RET_CONST(new Val(false, TYPE_BOOL))
 		uint32 p = atoi(yytext);
 		if ( p > 255 )
 			{
-			reporter->Error("bad port number -", yytext);
+			reporter->Error("bad port number - %s", yytext);
 			p = 0;
 			}
 		RET_CONST(new PortVal(p, TRANSPORT_ICMP))
@@ -435,7 +435,7 @@ F	RET_CONST(new Val(false, TYPE_BOOL))
 		uint32 p = atoi(yytext);
 		if ( p > 255 )
 			{
-			reporter->Error("bad port number -", yytext);
+			reporter->Error("bad port number - %s", yytext);
 			p = 0;
 			}
 		RET_CONST(new PortVal(p, TRANSPORT_UNKNOWN))
@@ -499,7 +499,7 @@ F	RET_CONST(new Val(false, TYPE_BOOL))
 
 <RE>[/\\\n]	return yytext[0];
 
-<*>.	reporter->Error("unrecognized character -", yytext);
+<*>.	reporter->Error("unrecognized character - %s", yytext);
 
 <<EOF>>	last_tok[0] = '\0'; return EOF;