diff --git a/src/m_specialpaths.cpp b/src/m_specialpaths.cpp
index 086f170f8..3e12be17d 100644
--- a/src/m_specialpaths.cpp
+++ b/src/m_specialpaths.cpp
@@ -146,6 +146,7 @@ FString M_GetCachePath(bool create)
 	// Don't use GAME_DIR and such so that ZDoom and its child ports can
 	// share the node cache.
 	path += "/zdoom/cache";
+	path.Substitute("//", "/");	// needed because progdir ends with a slash.
 	return path;
 }