diff --git a/lib-src/ChangeLog b/lib-src/ChangeLog
index 1b6a16dd524..424f3db53a1 100644
--- a/lib-src/ChangeLog
+++ b/lib-src/ChangeLog
@@ -1,3 +1,7 @@
+2010-07-23  Juanma Barranquero  <lekktu@gmail.com>
+
+	* make-docfile.c (write_c_args): Correctly handle prefixes of "defalt".
+
 2010-07-20  Juanma Barranquero  <lekktu@gmail.com>
 
 	* emacsclient.c (get_current_dir_name, w32_get_resource)
diff --git a/lib-src/make-docfile.c b/lib-src/make-docfile.c
index 51c30f91d8f..0b03b5e259d 100644
--- a/lib-src/make-docfile.c
+++ b/lib-src/make-docfile.c
@@ -488,7 +488,7 @@ write_c_args (FILE *out, char *func, char *buf, int minargs, int maxargs)
 
 	  /* In C code, `default' is a reserved word, so we spell it
 	     `defalt'; unmangle that here.  */
-	  if (strncmp (ident_start, "defalt", ident_length) == 0)
+	  if (ident_length == 6 && strncmp (ident_start, "defalt", 6) == 0)
 	    fprintf (out, "DEFAULT");
 	  else
 	    while (ident_length-- > 0)