diff --git a/dlls/dbghelp/Makefile.in b/dlls/dbghelp/Makefile.in
index c089d6598b3..65dba5fd821 100644
--- a/dlls/dbghelp/Makefile.in
+++ b/dlls/dbghelp/Makefile.in
@@ -4,6 +4,7 @@ SRCDIR    = @srcdir@
 VPATH     = @srcdir@
 MODULE    = dbghelp.dll
 IMPORTLIB = dbghelp
+EXTRADEFS = -D_IMAGEHLP_SOURCE_
 IMPORTS   = psapi kernel32 ntdll
 DELAYIMPORTS = version