diff --git a/.changes/unreleased/Fixed-20241126-195502.yaml b/.changes/unreleased/Fixed-20241126-195502.yaml
new file mode 100644
index 00000000..af460020
--- /dev/null
+++ b/.changes/unreleased/Fixed-20241126-195502.yaml
@@ -0,0 +1,3 @@
+kind: Fixed
+body: 'submit: Present a warning if submission might fail because of an unsubmitted base branch.'
+time: 2024-11-26T19:55:02.491968-08:00
diff --git a/branch_submit.go b/branch_submit.go
index bc19bf56..2c567dcc 100644
--- a/branch_submit.go
+++ b/branch_submit.go
@@ -190,12 +190,14 @@ func (cmd *branchSubmitCmd) run(
 	// Similarly, if the branch's base has a different name upstream,
 	// use that name instead.
 	upstreamBase := branch.Base
+	baseWasSubmitted := true
 	if branch.Base != store.Trunk() {
 		baseBranch, err := svc.LookupBranch(ctx, branch.Base)
 		if err != nil {
 			return fmt.Errorf("lookup base branch: %w", err)
 		}
 		upstreamBase = cmp.Or(baseBranch.UpstreamBranch, branch.Base)
+		baseWasSubmitted = baseBranch.Change != nil
 	}
 
 	var existingChange *forge.FindChangeItem
@@ -343,6 +345,13 @@ func (cmd *branchSubmitCmd) run(
 
 	// At this point, existingChange is nil only if we need to create a new CR.
 	if existingChange == nil {
+		// If we're definitely creating a new CR,
+		// make sure that the branch's base has been submitted.
+		if !baseWasSubmitted {
+			log.Warnf("%v: submit may fail: base %v has not been submitted",
+				cmd.Branch, upstreamBase)
+		}
+
 		if upstreamBranch == "" {
 			unique, err := svc.UnusedBranchName(ctx, remote, cmd.Branch)
 			if err != nil {
diff --git a/testdata/script/issue460_branch_submit_unsubmitted_base.txt b/testdata/script/issue460_branch_submit_unsubmitted_base.txt
new file mode 100644
index 00000000..60e0e6f9
--- /dev/null
+++ b/testdata/script/issue460_branch_submit_unsubmitted_base.txt
@@ -0,0 +1,35 @@
+# branch submit presents a good message when the base branch for a CR
+# hasn't been submitted yet.
+#
+# https://github.com/abhinav/git-spice/issues/460
+
+as 'Test <test@example.com>'
+at '2024-11-26T19:20:21Z'
+
+# setup
+cd repo
+git init
+git commit --allow-empty -m 'Initial commit'
+
+shamhub init
+shamhub new origin alice/example.git
+shamhub register alice
+git push origin main
+
+env SHAMHUB_USERNAME=alice
+gs auth login
+
+# set up main -> feat1 -> feat2
+git add feat1.txt
+gs bc -m feat1
+git add feat2.txt
+gs bc -m feat2
+
+# attempt to submit feat2
+! gs branch submit --fill
+stderr 'feat2: submit may fail: base feat1 has not been submitted'
+
+-- repo/feat1.txt --
+feat 1
+-- repo/feat2.txt --
+feat 2