diff --git a/repos/base-fiasco/lib/mk/kernel-fiasco.inc b/repos/base-fiasco/lib/mk/kernel-fiasco.inc
index 7638a7971..7a01b4712 100644
--- a/repos/base-fiasco/lib/mk/kernel-fiasco.inc
+++ b/repos/base-fiasco/lib/mk/kernel-fiasco.inc
@@ -20,8 +20,8 @@ $(FIASCO_BUILD_DIR):
 
 $(FIASCO): $(FIASCO_BUILD_DIR)
 	$(VERBOSE_MK) set -o pipefail; \
-	              MAKEFLAGS= CFLAGS="-std=gnu89" \
-	              CXXFLAGS="-std=gnu++98 -fno-delete-null-pointer-checks" \
+	              MAKEFLAGS= CFLAGS="-std=gnu89 $(CWARN)" \
+	              CXXFLAGS="-std=gnu++98 -fno-delete-null-pointer-checks $(CXXWARN)" \
 	              $(MAKE) SYSTEM_TARGET="$(CROSS_DEV_PREFIX)" \
 	                                 $(VERBOSE_DIR) -C $(FIASCO_BUILD_DIR) \
 	                                 $(KERNEL_BUILD_OUTPUT_FILTER)
diff --git a/repos/base-fiasco/lib/mk/l4_pkg.inc b/repos/base-fiasco/lib/mk/l4_pkg.inc
index 5f11b5459..36a6e8cfb 100644
--- a/repos/base-fiasco/lib/mk/l4_pkg.inc
+++ b/repos/base-fiasco/lib/mk/l4_pkg.inc
@@ -48,6 +48,14 @@ endif
 #
 .NOTPARALLEL: $(PKG_TAGS)
 
+WARN    = -Wno-attributes -Wno-cast-function-type -Wno-format-truncation \
+          -Wno-frame-address -Wno-ignored-qualifiers -Wno-implicit-fallthrough \
+          -Wno-maybe-uninitialized -Wno-misleading-indentation \
+          -Wno-nonnull-compare -Wno-nonnull-compare -Wno-restrict \
+          -Wno-tautological-compare -Wno-unused-but-set-variable -Wno-unused-result
+CWARN   = $(WARN) -Wno-int-conversion -Wno-pointer-sign -Wno-pointer-to-int-cast
+CXXWARN = $(WARN) -Wno-bool-compare -Wno-c++11-compat -Wno-class-memaccess
+
 #
 # The '_GNU_SOURCE' definition is needed to convince uClibc to define the
 # 'off64_t' type, which is used by bootstrap.
@@ -55,8 +63,8 @@ endif
 %.tag:
 	$(VERBOSE_MK) set -o pipefail; \
 	              MAKEFLAGS= CPPFLAGS="$(CC_MARCH)" \
-	              CFLAGS="$(CC_MARCH) -std=gnu89" \
-	              CXXFLAGS="$(CC_MARCH) -D_GNU_SOURCE -std=gnu++98" \
+	              CFLAGS="$(CC_MARCH) -std=gnu89 $(CWARN)" \
+	              CXXFLAGS="$(CC_MARCH) -D_GNU_SOURCE -std=gnu++98 $(CXXWARN)" \
 	              ASFLAGS="$(CC_MARCH)" LDFLAGS="$(LD_MARCH)" \
 	              $(MAKE) $(VERBOSE_DIR) O=$(L4_BUILD_DIR) $(L4_VERBOSE) \
 	                      -C $(L4_PKG_DIR)/$* \
diff --git a/repos/base-okl4/lib/mk/kernel-okl4.inc b/repos/base-okl4/lib/mk/kernel-okl4.inc
index e9583a53c..d1c3bf742 100644
--- a/repos/base-okl4/lib/mk/kernel-okl4.inc
+++ b/repos/base-okl4/lib/mk/kernel-okl4.inc
@@ -44,7 +44,8 @@ CC_OPT          += -DCONFIG_MAX_THREAD_BITS=10
 
 CC_OPT_PIC       =
 
-CC_CXX_WARN := -Wall -Wno-unused-but-set-variable -Wno-uninitialized
+CC_CXX_WARN := -Wall -Wno-unused-but-set-variable -Wno-uninitialized \
+               -Wno-register -Wno-unused-variable -Wno-tautological-compare
 
 #
 # Enforce building the kernel with -O3. Otherwise, the kernel build would fail
diff --git a/repos/base-pistachio/lib/mk/syscall-pistachio.mk b/repos/base-pistachio/lib/mk/syscall-pistachio.mk
index 787b3bb5b..4631c9bb0 100644
--- a/repos/base-pistachio/lib/mk/syscall-pistachio.mk
+++ b/repos/base-pistachio/lib/mk/syscall-pistachio.mk
@@ -4,7 +4,8 @@ PISTACHIO_USER_SRC    := $(PISTACHIO_CONTRIB_DIR)/user/lib/l4
 LD_PREFIX := "-Wl,"
 
 CC_WARN += -Wno-array-bounds -Wno-unused-but-set-variable \
-           -Wno-parentheses -Wno-format
+           -Wno-parentheses -Wno-format -Wno-builtin-declaration-mismatch \
+           -Wno-unused-function -Wno-pointer-compare
 
 user_build.tag:
 	LIBGCCFLAGS="$(CC_MARCH)" \