diff --git a/mk/check.mk b/mk/check.mk
index fbc2592d46a..03e6e49be3a 100644
--- a/mk/check.mk
+++ b/mk/check.mk
@@ -26,11 +26,14 @@ reftest: $(S)src/reftest/reftest.rs servo
 contenttest: $(S)src/contenttest/contenttest.rs servo
 	$(RUSTC) $(RFLAGS_servo) -o $@ $< -L .
 
-.PHONY: check $(DEPS_CHECK_ALL)
+DEPS_CHECK_TARGETS_ALL = $(addprefix check-,$(DEPS_CHECK_ALL))
+DEPS_CHECK_TARGETS_FAST = $(addprefix check-,$(filter-out $(SLOW_TESTS),$(DEPS_CHECK_ALL)))
 
-check: $(addprefix check-,$(filter-out $(SLOW_TESTS),$(DEPS_CHECK_ALL))) check-servo
+.PHONY: check $(DEPS_CHECK_TARGETS_ALL)
 
-check-all: $(addprefix check-,$(DEPS_CHECK_ALL)) check-servo
+check: $(DEPS_CHECK_TARGETS_FAST) check-servo
+
+check-all: $(DEPS_CHECK_TARGETS_ALL) check-servo
 
 check-servo: servo-test
 	./servo-test $(TESTNAME)
diff --git a/mk/clean.mk b/mk/clean.mk
index bc6fee79478..764a0d611aa 100644
--- a/mk/clean.mk
+++ b/mk/clean.mk
@@ -6,15 +6,24 @@ clean-$(1) :
 	$$(Q)$$(MAKE) -C $$(B)src/$(1) clean
 
 # add these targets to meta-targets
-DEPS_CLEAN += clean-$(1)
+DEPS_CLEAN_ALL += $(1)
 endef
 
 $(foreach submodule,$(CFG_SUBMODULES),\
 $(eval $(call DEF_SUBMODULE_CLEAN_RULES,$(submodule))))
 
-.PHONY:	clean $(DEPS_CLEAN)
+DEPS_CLEAN_TARGETS_ALL = $(addprefix clean-,$(DEPS_CLEAN_ALL))
+DEPS_CLEAN_TARGETS_FAST = $(addprefix clean-,$(filter-out $(SLOW_BUILDS),$(DEPS_CLEAN_ALL)))
 
-clean: $(DEPS_CLEAN) clean-servo
+.PHONY:	clean $(DEPS_CLEAN_TARGETS_ALL)
+
+clean: $(DEPS_CLEAN_TARGETS_ALL) clean-servo
+	$(Q)echo "Cleaning targets:"
+	$(Q)echo "$(DEPS_CLEAN_ALL)"
+
+clean-fast: $(DEPS_CLEAN_TARGETS_FAST) clean-servo
+	$(Q)echo "Cleaning targets:"
+	$(Q)echo "$(filter-out $(SLOW_BUILDS),$(DEPS_CLEAN_ALL))"
 
 clean-servo:
 	rm -f servo servo-test
diff --git a/mk/sub.mk b/mk/sub.mk
index 8b6a6e4019c..ac1206fed61 100644
--- a/mk/sub.mk
+++ b/mk/sub.mk
@@ -3,6 +3,15 @@ SLOW_TESTS += \
 	mozjs \
 	$(NULL)
 
+# These submodules will not be cleaned by the `make clean-fast` target.
+SLOW_BUILDS += \
+	libcss \
+	libparserutils \
+	libwapcaplet \
+	mozjs \
+	sharegl \
+	skia \
+	$(NULL)
 
 # NOTE: the make magic can only compute transitive build dependencies,
 # not transitive link flags. So, if A -> B -> C, must add A as a dep