diff --git a/defs/gmake.mk b/defs/gmake.mk
index baea0dc02f..d234791d13 100644
--- a/defs/gmake.mk
+++ b/defs/gmake.mk
@@ -196,8 +196,8 @@ update-github: fetch-github
 	  curl -s $(if $(GITHUB_TOKEN),-H "Authorization: bearer $(GITHUB_TOKEN)") $(PULL_REQUEST_API) | \
 	  $(BASERUBY) -rjson -e 'JSON.parse(STDIN.read)["head"].tap { |h| print "#{h["repo"]["full_name"]} #{h["ref"]}" }' \
 	))
-	$(eval FORK_REPO := $(shell echo $(PULL_REQUEST_FORK_BRANCH) | cut -d' ' -f1))
-	$(eval PR_BRANCH := $(shell echo $(PULL_REQUEST_FORK_BRANCH) | cut -d' ' -f2))
+	$(eval FORK_REPO := $(word 1,$(PULL_REQUEST_FORK_BRANCH)))
+	$(eval PR_BRANCH := $(word 2,$(PULL_REQUEST_FORK_BRANCH)))
 
 	$(eval GITHUB_UPDATE_WORKTREE := $(shell mktemp -d "$(srcdir)/gh-$(PR)-XXXXXX"))
 	git -C "$(srcdir)" worktree add $(notdir $(GITHUB_UPDATE_WORKTREE)) "gh-$(PR)"