diff --git a/libc/malloc_debug/FreeTrackData.h b/libc/malloc_debug/FreeTrackData.h
index 21f845f..1758ef5 100644
--- a/libc/malloc_debug/FreeTrackData.h
+++ b/libc/malloc_debug/FreeTrackData.h
@@ -42,7 +42,7 @@
 
 // Forward declarations.
 struct BacktraceHeader;
-struct Config;
+class Config;
 class DebugData;
 struct Header;