diff --git a/builtin/rebase.c b/builtin/rebase.c
index 96ffa80b7119e4436c5d078e157e530fb5af670f..571cf899d5b48c87c3c2f1d91d2d94e559bcfd68 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1064,12 +1064,22 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	for (i = 0; i < options.git_am_opts.argc; i++) {
-		const char *option = options.git_am_opts.argv[i];
+		const char *option = options.git_am_opts.argv[i], *p;
 		if (!strcmp(option, "--committer-date-is-author-date") ||
 		    !strcmp(option, "--ignore-date") ||
 		    !strcmp(option, "--whitespace=fix") ||
 		    !strcmp(option, "--whitespace=strip"))
 			options.flags |= REBASE_FORCE;
+		else if (skip_prefix(option, "-C", &p)) {
+			while (*p)
+				if (!isdigit(*(p++)))
+					die(_("switch `C' expects a "
+					      "numerical value"));
+		} else if (skip_prefix(option, "--whitespace=", &p)) {
+			if (*p && strcmp(p, "warn") && strcmp(p, "nowarn") &&
+			    strcmp(p, "error") && strcmp(p, "error-all"))
+				die("Invalid whitespace option: '%s'", p);
+		}
 	}
 
 	if (!(options.flags & REBASE_NO_QUIET))
diff --git a/t/t3406-rebase-message.sh b/t/t3406-rebase-message.sh
index 0392e36d2364c8149f2a628a0901f113b7a5875f..2c79eed4febda6977dde4d530d73a184cfa92d80 100755
--- a/t/t3406-rebase-message.sh
+++ b/t/t3406-rebase-message.sh
@@ -84,4 +84,11 @@ test_expect_success 'rebase --onto outputs the invalid ref' '
 	test_i18ngrep "invalid-ref" err
 '
 
+test_expect_success 'error out early upon -C<n> or --whitespace=<bad>' '
+	test_must_fail git rebase -Cnot-a-number HEAD 2>err &&
+	test_i18ngrep "numerical value" err &&
+	test_must_fail git rebase --whitespace=bad HEAD 2>err &&
+	test_i18ngrep "Invalid whitespace option" err
+'
+
 test_done