diff --git a/contrib/generate_precompile.jl b/contrib/generate_precompile.jl
index e6cf280812685..a10d195229cab 100644
--- a/contrib/generate_precompile.jl
+++ b/contrib/generate_precompile.jl
@@ -1,5 +1,9 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
+if Threads.nthreads() != 1
+    @warn "Running this file with multiple Julia threads may lead to a build error" Threads.nthreads()
+end
+
 if Base.isempty(Base.ARGS) || Base.ARGS[1] !== "0"
 Sys.__init_build()
 # Prevent this from being put into the Main namespace
diff --git a/sysimage.mk b/sysimage.mk
index de5c3e22f253a..1586eb7dbc16d 100644
--- a/sysimage.mk
+++ b/sysimage.mk
@@ -77,6 +77,7 @@ define sysimg_builder
 $$(build_private_libdir)/sys$1-o.a $$(build_private_libdir)/sys$1-bc.a : $$(build_private_libdir)/sys$1-%.a : $$(build_private_libdir)/sys.ji
 	@$$(call PRINT_JULIA, cd $$(JULIAHOME)/base && \
 	if ! JULIA_BINDIR=$$(call cygpath_w,$(build_bindir)) WINEPATH="$$(call cygpath_w,$$(build_bindir));$$$$WINEPATH" \
+			JULIA_NUM_THREADS=1 \
 			$$(call spawn, $3) $2 -C "$$(JULIA_CPU_TARGET)" --output-$$* $$(call cygpath_w,$$@).tmp $$(JULIA_SYSIMG_BUILD_FLAGS) \
 			--startup-file=no --warn-overwrite=yes --sysimage $$(call cygpath_w,$$<) $$(call cygpath_w,$$(JULIAHOME)/contrib/generate_precompile.jl) $(JULIA_PRECOMPILE); then \
 		echo '*** This error is usually fixed by running `make clean`. If the error persists$$(COMMA) try `make cleanall`. ***'; \