diff --git a/spec/interfaceToC.dd b/spec/interfaceToC.dd
index 253595b7ac..7f18cc99c0 100644
--- a/spec/interfaceToC.dd
+++ b/spec/interfaceToC.dd
@@ -25,7 +25,7 @@ $(H2 $(LNAME2 calling_c_functions, Calling C Functions))
 	)
 
 ------
-extern (C) int strcmp(char* string1, char* string2);
+extern (C) int strcmp(const char* string1, const char* string2);
 ------
 
 	$(P and then it can be called within D code in the obvious way:)