diff --git a/Makefile b/Makefile
index 92f0bda5e..b8ca504f0 100644
--- a/Makefile
+++ b/Makefile
@@ -246,7 +246,7 @@ ifdef NEEDS_NSL
 	SIMPLE_LIB += -lnsl
 endif
 ifdef NO_STRCASESTR
-	DEFINES += -Dstrcasestr=gitstrcasestr
+	DEFINES += -Dstrcasestr=gitstrcasestr -DNO_STRCASESTR=1
 	LIB_OBJS += compat/strcasestr.o
 endif
 
diff --git a/mailinfo.c b/mailinfo.c
index df470bb9c..cb853df99 100644
--- a/mailinfo.c
+++ b/mailinfo.c
@@ -9,6 +9,10 @@
 #include <ctype.h>
 #include <iconv.h>
 
+#ifdef NO_STRCASESTR
+extern char *gitstrcasestr(const char *haystack, const char *needle);
+#endif
+
 static FILE *cmitmsg, *patchfile;
 
 static int keep_subject = 0;