diff --git a/src/makeb32.env b/src/makeb32.env
index 739cc9a2ad..0f942ef87d 100644
--- a/src/makeb32.env
+++ b/src/makeb32.env
@@ -137,7 +137,7 @@ LINK_FLAGS= /Tpd /c $(EXTRALINKFLAGS)
 !endif
 
 CFG=$(CFG).cfg
-CPPFLAGS=$(CPPFLAGS) $(DLL_FLAGS) $(EXTRACPPFLAGS) @$(CFG)
+CPPFLAGS=$(CPPFLAGS) $(DLL_FLAGS) @$(CFG) $(EXTRACPPFLAGS)
 
 DUMMY=dummy
 
diff --git a/src/png/makefile.b32 b/src/png/makefile.b32
index 024c80439d..19fb0727b7 100644
--- a/src/png/makefile.b32
+++ b/src/png/makefile.b32
@@ -17,5 +17,9 @@ OBJECTS = png.obj pngread.obj pngrtran.obj pngrutil.obj \
           pngpread.obj pngtrans.obj pngwrite.obj pngwtran.obj pngwutil.obj \
           pngerror.obj pngmem.obj pngwio.obj pngrio.obj pngget.obj pngset.obj
 
+# Precompiled headers seem to interfere with correct compilation
+# of png library, so switch them off
+EXTRACPPFLAGS=-H-
+
 !include $(WXWIN)\src\makelib.b32