diff --git a/utils/path.c b/utils/path.c
index 26c678f2..70573260 100644
--- a/utils/path.c
+++ b/utils/path.c
@@ -108,7 +108,7 @@ PaCheckCompressed(filename)
  *	newstring is the new string to append to the path.
  */
 void
-PaAppend(char **pathptr, char *newstring)
+PaAppend(char **pathptr, const char *newstring)
 {
     int oldlength, addlength;
     char *new;
diff --git a/utils/utils.h b/utils/utils.h
index d3ece6d8..a74c75c0 100644
--- a/utils/utils.h
+++ b/utils/utils.h
@@ -58,7 +58,7 @@ extern bool StrIsInt(const char *);
 extern bool StrIsNumeric(const char *);
 
 /* C99 compat */
-extern void PaAppend(char **, char *);
+extern void PaAppend(char **pathptr, const char *newstring);
 extern void ReduceFraction(int *, int *);
 extern bool TechLoad(char *, SectionID);
 extern void UndoFlush();