--- a/client.mk
+++ b/client.mk
@@ -137,16 +137,19 @@ ifdef MOZ_PARALLEL_BUILD
 endif
 
 # Automatically add -jN to make flags if not defined. N defaults to number of cores.
 ifeq (,$(findstring -j,$(MOZ_MAKE_FLAGS)))
   cores=$(shell $(PYTHON) -c 'import multiprocessing; print(multiprocessing.cpu_count())')
   MOZ_MAKE_FLAGS += -j$(cores)
 endif
 
+ifeq (4.0,$(firstword $(sort 4.0 $(MAKE_VERSION))))
+MOZ_MAKE_FLAGS += --output-sync=line
+endif
 
 ifdef MOZ_BUILD_PROJECTS
 
 ifdef MOZ_CURRENT_PROJECT
   BUILD_PROJECT_ARG = MOZ_BUILD_APP=$(MOZ_CURRENT_PROJECT)
   export MOZ_CURRENT_PROJECT
 else
   MOZ_MAKE = $(error Cannot build in the OBJDIR when MOZ_CURRENT_PROJECT is not set.)