diff --git a/GNUmakefile b/GNUmakefile
index b7dd2a24..f718b73e 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -32,10 +32,10 @@ ifndef ARCH
 endif
 
 libui:
-	@$(MAKE) -f GNUmakefile.libui OS=$(OS) ARCH=$(ARCH) OUTDIR=$(OUTDIR) OBJDIR=$(OBJDIR)
+	@$(MAKE) -f GNUmakefile.libui OS=$(OS) ARCH=$(ARCH) OUTDIR=$(OUTDIR) OBJDIR=$(OBJDIR) inlibuibuild=1
 
 clean:
-	@$(MAKE) -f GNUmakefile.libui OS=$(OS) ARCH=$(ARCH) OUTDIR=$(OUTDIR) OBJDIR=$(OBJDIR) clean
+	@$(MAKE) -f GNUmakefile.libui OS=$(OS) ARCH=$(ARCH) OUTDIR=$(OUTDIR) OBJDIR=$(OBJDIR) inlibuibuild=1 clean
 
 test: libui
-	@$(MAKE) -f GNUmakefile.test OS=$(OS) ARCH=$(ARCH) OUTDIR=$(OUTDIR) OBJDIR=$(OBJDIR)
+	@$(MAKE) -f GNUmakefile.test OS=$(OS) ARCH=$(ARCH) OUTDIR=$(OUTDIR) OBJDIR=$(OBJDIR) inlibuibuild=1
diff --git a/GNUmakefile.libui b/GNUmakefile.libui
index 496c48a0..628f10fc 100644
--- a/GNUmakefile.libui
+++ b/GNUmakefile.libui
@@ -1,5 +1,9 @@
 # 16 october 2015
 
+ifndef inlibuibuild
+$(error [FAIL] do not run these makefiles directly)
+endif
+
 include $(OS)/GNUosspecific.mk
 include common/GNUmakeinc.mk
 include $(OS)/GNUmakeinc.mk
diff --git a/GNUmakefile.test b/GNUmakefile.test
index 0f2c69c8..c074b892 100644
--- a/GNUmakefile.test
+++ b/GNUmakefile.test
@@ -1,5 +1,9 @@
 # 16 october 2015
 
+ifndef inlibuibuild
+$(error [FAIL] do not run these makefiles directly)
+endif
+
 include $(OS)/GNUosspecific.mk
 include test/GNUmakeinc.mk
 
diff --git a/windows/GNUosspecific.mk b/windows/GNUosspecific.mk
index 313061d3..f2168845 100644
--- a/windows/GNUosspecific.mk
+++ b/windows/GNUosspecific.mk
@@ -11,5 +11,5 @@ else ifeq ($(ARCH),386)
 	CC = i686-w64-mingw32-gcc
 	RC = i686-w64-mingw32-windres
 else ifneq ($(ARCH),default)
-	$(error [FAIL] unknown architecture $(ARCH))
+$(error [FAIL] unknown architecture $(ARCH))
 endif