diff --git a/src/dcfg.c b/src/dcfg.c
index 333e9f2..e727e17 100644
--- a/src/dcfg.c
+++ b/src/dcfg.c
@@ -364,6 +364,7 @@ static void *alloc(size_t size) { return calloc(1, size); }
 #endif
 
 #if DCFG_POSIX_SUPPORT
+char *realpath(char const *, char *);
 static char *realpath_(char const *s)
 {
 	char buf[PATH_MAX];