diff --git a/routers/api/v1/repo/pull.go b/routers/api/v1/repo/pull.go
index ef86f413b7..ef8cc6cd93 100644
--- a/routers/api/v1/repo/pull.go
+++ b/routers/api/v1/repo/pull.go
@@ -22,6 +22,7 @@ import (
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/git/gitcmd"
 	"code.gitea.io/gitea/modules/gitrepo"
 	"code.gitea.io/gitea/modules/graceful"
 	"code.gitea.io/gitea/modules/log"
@@ -1429,7 +1430,11 @@ func GetPullRequestCommits(ctx *context.APIContext) {
 	} else {
 		compareInfo, err = git_service.GetCompareInfo(ctx, pr.BaseRepo, pr.BaseRepo, baseGitRepo, git.RefNameFromBranch(pr.BaseBranch), git.RefName(pr.GetGitHeadRefName()), false, false)
 	}
-	if err != nil {
+
+	if gitcmd.StderrHasPrefix(err, "fatal: bad revision") {
+		ctx.APIError(http.StatusNotFound, "invalid base branch or revision")
+		return
+	} else if err != nil {
 		ctx.APIErrorInternal(err)
 		return
 	}