diff --git a/lib/fs/rules.mk b/lib/fs/rules.mk
index 230c32bf..2f589d59 100644
--- a/lib/fs/rules.mk
+++ b/lib/fs/rules.mk
@@ -6,7 +6,7 @@ MODULE_SRCS += $(LOCAL_DIR)/debug.c
 MODULE_SRCS += $(LOCAL_DIR)/fs.c
 MODULE_SRCS += $(LOCAL_DIR)/shell.c
 
-ifeq ($(call TOBOOL,WITH_TESTS),true)
+ifeq ($(call TOBOOL,$(WITH_TESTS)),true)
 MODULE_DEPS += $(LOCAL_DIR)/test
 endif
 
diff --git a/lib/fs/spifs/rules.mk b/lib/fs/spifs/rules.mk
index 25c196c3..7852f700 100644
--- a/lib/fs/spifs/rules.mk
+++ b/lib/fs/spifs/rules.mk
@@ -4,7 +4,7 @@ MODULE := $(LOCAL_DIR)
 
 MODULE_SRCS += $(LOCAL_DIR)/spifs.c
 
-ifeq ($(call TOBOOL,WITH_TESTS),true)
+ifeq ($(call TOBOOL,$(WITH_TESTS)),true)
 MODULE_DEPS += $(LOCAL_DIR)/test
 endif
 
diff --git a/lib/libc/rules.mk b/lib/libc/rules.mk
index a839c424..cb647b66 100644
--- a/lib/libc/rules.mk
+++ b/lib/libc/rules.mk
@@ -28,7 +28,7 @@ MODULE_COMPILEFLAGS += -fno-builtin
 
 MODULE_OPTIONS := extra_warnings
 
-ifeq ($(call TOBOOL,WITH_TESTS),true)
+ifeq ($(call TOBOOL,$(WITH_TESTS)),true)
 MODULE_DEPS += $(LOCAL_DIR)/test
 endif