--- old/make/Init.gmk	2018-04-19 17:44:07.349689850 +0200
+++ new/make/Init.gmk	2018-04-19 17:44:06.950691146 +0200
@@ -310,9 +310,13 @@
           ifneq ($(PARALLEL_TARGETS), )
 	    $(call StartGlobalTimer)
 	    $(call PrepareSmartJavac)
+            # JOBS will only be empty for a bootcycle-images recursive call
+            # or if specified via a make argument directly. In those cases
+            # treat it as NOT using jobs at all.
 	    ( cd $(TOPDIR) && \
 	        $(NICE) $(MAKE) $(MAKE_ARGS) $(OUTPUT_SYNC_FLAG) \
-	            -j $(JOBS) -f make/Main.gmk $(USER_MAKE_VARS) \
+                    $(if $(JOBS), -j $(JOBS)) \
+	            -f make/Main.gmk $(USER_MAKE_VARS) \
 	            $(PARALLEL_TARGETS) $(COMPARE_BUILD_MAKE) $(BUILD_LOG_PIPE) || \
 	        ( exitcode=$$? && \
 	        $(PRINTF) "\nERROR: Build failed for $(TARGET_DESCRIPTION) (exit code $$exitcode) \n" \