diff --git a/lib/libinternal.h b/lib/libinternal.h
index 224d5e1..9d669d7 100644
--- a/lib/libinternal.h
+++ b/lib/libinternal.h
@@ -53,7 +53,7 @@
 #define debug_ptr(a)    if(!(a))fprintf(stderr," ** NULL pointer: " __FILE__ ", line %d\n",__LINE__);
 #define debug_int(a)    if((a)<0)fprintf(stderr," ** error: " __FILE__ ", line %d\n",__LINE__);
 
-#define COMEDILIB_DEBUG(level,format,args...) do{if(__comedi_loglevel>=(level))fprintf(stderr,__FUNCTION__ ": " format, ## args);}while(0)
+#define COMEDILIB_DEBUG(level,format,args...) do{if(__comedi_loglevel>=(level))fprintf(stderr,"%s: " format, __FUNCTION__, ## args);}while(0)
 
 #define COMEDI_VERSION_CODE(a,b,c) (((a)<<16) | ((b)<<8) | (c))