--- a/aux/broctl/aux/pysubnettree/SubnetTree_wrap.cc
+++ b/aux/broctl/aux/pysubnettree/SubnetTree_wrap.cc
@@ -867,7 +867,7 @@ SWIG_Python_AddErrorMsg(const char* mesg)
     Py_DECREF(old_str);
     Py_DECREF(value);
   } else {
-    PyErr_Format(PyExc_RuntimeError, mesg);
+    PyErr_Format(PyExc_RuntimeError, "%s", mesg);
   }
 }
 
--- a/aux/nftools/ftwire2bro.c
+++ b/aux/nftools/ftwire2bro.c
@@ -13,7 +13,7 @@
 #include "nfcommon.h"
 
 void leave (int errlvl, const char *msg) {
-  fprintf (stderr, msg);
+  fprintf (stderr, "%s", msg);
   exit (errlvl);
 }
 
--- a/src/DCE_RPC.cc
+++ b/src/DCE_RPC.cc
@@ -82,7 +82,7 @@ UUID::UUID(const char* str)
 		}
 
 	if ( i != 16 )
-		internal_error(fmt("invalid UUID string: %s", str));
+		internal_error("invalid UUID string: %s", str);
 	}
 
 typedef map<UUID, BroEnum::dce_rpc_if_id> uuid_map_t;
--- a/src/PrefixTable.cc
+++ b/src/PrefixTable.cc
@@ -99,8 +99,8 @@ void* PrefixTable::Lookup(const Val* value, bool exact) const
 		break;
 
 	default:
-		internal_error(fmt("Wrong index type %d for PrefixTable",
-					value->Type()->Tag()));
+		internal_error("Wrong index type %d for PrefixTable",
+					value->Type()->Tag());
 		return 0;
 	}
 	}
--- a/src/RemoteSerializer.cc
+++ b/src/RemoteSerializer.cc
@@ -2711,7 +2711,7 @@ void RemoteSerializer::InternalCommError(const char* msg)
 #ifdef DEBUG_COMMUNICATION
 	DumpDebugData();
 #else
-	internal_error(msg);
+	internal_error("%s", msg);
 #endif
 	}
 
@@ -3061,7 +3061,7 @@ bool SocketComm::ProcessParentMessage()
 			}
 
 		default:
-			internal_error(fmt("unknown msg type %d", parent_msgtype));
+			internal_error("unknown msg type %d", parent_msgtype);
 			return true;
 		}
 
--- a/src/SerialObj.cc
+++ b/src/SerialObj.cc
@@ -47,7 +47,7 @@ void SerialObj::Register(SerialType type, FactoryFunc f, const char* name)
 
 	FactoryMap::iterator i = factories->find(type);
 	if ( i != factories->end() )
-		internal_error(fmt("SerialType 0x%08x registered twice", type));
+		internal_error("SerialType 0x%08x registered twice", type);
 
 	(*factories)[type] = f;
 	(*names)[type] = name;
--- a/src/Sessions.cc
+++ b/src/Sessions.cc
@@ -968,7 +968,7 @@ void NetSessions::Remove(Connection* c)
 				;
 
 			else if ( ! tcp_conns.RemoveEntry(k) )
-				internal_error(fmt("connection missing"));
+				internal_error("connection missing");
 			break;
 
 		case TRANSPORT_UDP:
@@ -1354,7 +1354,7 @@ void NetSessions::Internal(const char* msg, const struct pcap_pkthdr* hdr,
 				const u_char* pkt)
 	{
 	DumpPacket(hdr, pkt);
-	internal_error(msg);
+	internal_error("%s", msg);
 	}
 
 void NetSessions::Weird(const char* name,