diff --git a/src/proto.h b/src/proto.h
index a8faa83..74f38cd 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -119,7 +119,7 @@
 // These prototypes cannot be produced automatically.
 int smsg(const char *, ...)
 # ifdef USE_PRINTF_FORMAT_ATTRIBUTE
-    __attribute__((format(printf, 1, 0)))
+    __attribute__((format(printf, 1, 2)))
 # endif
     ;
 
@@ -138,14 +138,14 @@
 // These prototypes cannot be produced automatically.
 int semsg(const char *, ...)
 # ifdef USE_PRINTF_FORMAT_ATTRIBUTE
-    __attribute__((format(printf, 1, 0)))
+    __attribute__((format(printf, 1, 2)))
 # endif
     ;
 
 // These prototypes cannot be produced automatically.
 void siemsg(const char *, ...)
 # ifdef USE_PRINTF_FORMAT_ATTRIBUTE
-    __attribute__((format(printf, 1, 0)))
+    __attribute__((format(printf, 1, 2)))
 # endif
     ;