Index: uspace/Makefile.common
===================================================================
--- uspace/Makefile.common	(revision 09ab0a9afc9379f1604c0fd75cac2d9287ba022c)
+++ uspace/Makefile.common	(revision 7570a95fbe39d85de25c810a36eb504d2e33eb6d)
@@ -99,10 +99,10 @@
 LIBC_PREFIX = $(LIB_PREFIX)/c
 LIBC_INCLUDES_FLAGS = \
-	-I$(LIBC_PREFIX)/include \
-	-I$(LIBC_PREFIX)/arch/$(UARCH)/include \
-	-I$(ROOT_PATH)/abi/include
+	-isystem $(LIBC_PREFIX)/include \
+	-isystem $(LIBC_PREFIX)/arch/$(UARCH)/include \
+	-isystem $(ROOT_PATH)/abi/include
 
 LIBCPP_PREFIX = $(LIB_PREFIX)/cpp
-LIBCPP_INCLUDES_FLAGS = -I$(LIBCPP_PREFIX)/include
+LIBCPP_INCLUDES_FLAGS = -isystem $(LIBCPP_PREFIX)/include
 
 LIBDLTEST_PREFIX = $(LIB_PREFIX)/dltest
@@ -184,5 +184,7 @@
 	-Wmissing-prototypes \
 	-Wwrite-strings \
-	-Werror-implicit-function-declaration
+	-Werror-implicit-function-declaration \
+	-Wsystem-headers \
+	-Wunknown-pragmas
 
 # XXX: -fno-builtin-strftime is for a seemingly spurious format warning.