diff --git a/Makefile b/Makefile
index 49bea7b..8df4c35 100644
--- a/Makefile
+++ b/Makefile
@@ -746,7 +746,7 @@ $(BUILD)/ndk-include_ndk13: $(BUILD)/ndk-include_ndk $(BUILD)/fd2sfd/_done $(BUI
 	$(L0)"extract ndk13"$(L1) while read p; do p=$$(echo $$p|tr -d '\n'); \
 	  mkdir -p $(PREFIX)/m68k-amigaos/ndk13-include/$$(dirname $$p); \
 	  if grep V36 $(PREFIX)/m68k-amigaos/ndk-include/$$p; then \
-	  LC_CTYPE=C sed -n -e '/#ifndef\s\s*CLIB/,/V36/p' $(PREFIX)/m68k-amigaos/ndk-include/$$p >$(PREFIX)/m68k-amigaos/ndk13-include/$$p; \
+	  LC_CTYPE=C sed -n -e '/#ifndef[[:space:]]*CLIB/,/V36/p' $(PREFIX)/m68k-amigaos/ndk-include/$$p >$(PREFIX)/m68k-amigaos/ndk13-include/$$p; \
 	  echo -e "#ifdef __cplusplus\n}\n#endif /* __cplusplus */\n#endif" >>$(PREFIX)/m68k-amigaos/ndk13-include/$$p; \
 	  else cp $(PREFIX)/m68k-amigaos/ndk-include/$$p $(PREFIX)/m68k-amigaos/ndk13-include/$$p; fi \
 	done < patches/ndk13/chfiles $(L2)