diff --git a/fast-import.c b/fast-import.c
index a85275d..eed97c8 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -2207,6 +2207,59 @@
 	return do_change_note_fanout(root, root, hex_sha1, 0, path, 0, fanout);
 }
 
+/*
+ * Given a pointer into a string, parse a mark reference:
+ *
+ *   idnum ::= ':' bigint;
+ *
+ * Return the first character after the value in *endptr.
+ *
+ * Complain if the following character is not what is expected,
+ * either a space or end of the string.
+ */
+static uintmax_t parse_mark_ref(const char *p, char **endptr)
+{
+	uintmax_t mark;
+
+	assert(*p == ':');
+	p++;
+	mark = strtoumax(p, endptr, 10);
+	if (*endptr == p)
+		die("No value after ':' in mark: %s", command_buf.buf);
+	return mark;
+}
+
+/*
+ * Parse the mark reference, and complain if this is not the end of
+ * the string.
+ */
+static uintmax_t parse_mark_ref_eol(const char *p)
+{
+	char *end;
+	uintmax_t mark;
+
+	mark = parse_mark_ref(p, &end);
+	if (*end != '\0')
+		die("Garbage after mark: %s", command_buf.buf);
+	return mark;
+}
+
+/*
+ * Parse the mark reference, demanding a trailing space.  Return a
+ * pointer to the space.
+ */
+static uintmax_t parse_mark_ref_space(const char **p)
+{
+	uintmax_t mark;
+	char *end;
+
+	mark = parse_mark_ref(*p, &end);
+	if (*end != ' ')
+		die("Missing space after mark: %s", command_buf.buf);
+	*p = end;
+	return mark;
+}
+
 static void file_change_m(struct branch *b)
 {
 	const char *p = command_buf.buf + 2;
@@ -2235,21 +2288,21 @@
 	}
 
 	if (*p == ':') {
-		char *x;
-		oe = find_mark(strtoumax(p + 1, &x, 10));
+		oe = find_mark(parse_mark_ref_space(&p));
 		hashcpy(sha1, oe->idx.sha1);
-		p = x;
-	} else if (!prefixcmp(p, "inline")) {
+	} else if (!prefixcmp(p, "inline ")) {
 		inline_data = 1;
-		p += 6;
+		p += strlen("inline");  /* advance to space */
 	} else {
 		if (get_sha1_hex(p, sha1))
-			die("Invalid SHA1: %s", command_buf.buf);
+			die("Invalid dataref: %s", command_buf.buf);
 		oe = find_object(sha1);
 		p += 40;
+		if (*p != ' ')
+			die("Missing space after SHA1: %s", command_buf.buf);
 	}
-	if (*p++ != ' ')
-		die("Missing space after SHA1: %s", command_buf.buf);
+	assert(*p == ' ');
+	p++;  /* skip space */
 
 	strbuf_reset(&uq);
 	if (!unquote_c_style(&uq, p, &endp)) {
@@ -2407,21 +2460,21 @@
 	/* Now parse the notemodify command. */
 	/* <dataref> or 'inline' */
 	if (*p == ':') {
-		char *x;
-		oe = find_mark(strtoumax(p + 1, &x, 10));
+		oe = find_mark(parse_mark_ref_space(&p));
 		hashcpy(sha1, oe->idx.sha1);
-		p = x;
-	} else if (!prefixcmp(p, "inline")) {
+	} else if (!prefixcmp(p, "inline ")) {
 		inline_data = 1;
-		p += 6;
+		p += strlen("inline");  /* advance to space */
 	} else {
 		if (get_sha1_hex(p, sha1))
-			die("Invalid SHA1: %s", command_buf.buf);
+			die("Invalid dataref: %s", command_buf.buf);
 		oe = find_object(sha1);
 		p += 40;
+		if (*p != ' ')
+			die("Missing space after SHA1: %s", command_buf.buf);
 	}
-	if (*p++ != ' ')
-		die("Missing space after SHA1: %s", command_buf.buf);
+	assert(*p == ' ');
+	p++;  /* skip space */
 
 	/* <committish> */
 	s = lookup_branch(p);
@@ -2430,7 +2483,7 @@
 			die("Can't add a note on empty branch.");
 		hashcpy(commit_sha1, s->sha1);
 	} else if (*p == ':') {
-		uintmax_t commit_mark = strtoumax(p + 1, NULL, 10);
+		uintmax_t commit_mark = parse_mark_ref_eol(p);
 		struct object_entry *commit_oe = find_mark(commit_mark);
 		if (commit_oe->type != OBJ_COMMIT)
 			die("Mark :%" PRIuMAX " not a commit", commit_mark);
@@ -2537,7 +2590,7 @@
 		hashcpy(b->branch_tree.versions[0].sha1, t);
 		hashcpy(b->branch_tree.versions[1].sha1, t);
 	} else if (*from == ':') {
-		uintmax_t idnum = strtoumax(from + 1, NULL, 10);
+		uintmax_t idnum = parse_mark_ref_eol(from);
 		struct object_entry *oe = find_mark(idnum);
 		if (oe->type != OBJ_COMMIT)
 			die("Mark :%" PRIuMAX " not a commit", idnum);
@@ -2572,7 +2625,7 @@
 		if (s)
 			hashcpy(n->sha1, s->sha1);
 		else if (*from == ':') {
-			uintmax_t idnum = strtoumax(from + 1, NULL, 10);
+			uintmax_t idnum = parse_mark_ref_eol(from);
 			struct object_entry *oe = find_mark(idnum);
 			if (oe->type != OBJ_COMMIT)
 				die("Mark :%" PRIuMAX " not a commit", idnum);
@@ -2735,7 +2788,7 @@
 		type = OBJ_COMMIT;
 	} else if (*from == ':') {
 		struct object_entry *oe;
-		from_mark = strtoumax(from + 1, NULL, 10);
+		from_mark = parse_mark_ref_eol(from);
 		oe = find_mark(from_mark);
 		type = oe->type;
 		hashcpy(sha1, oe->idx.sha1);
@@ -2867,18 +2920,13 @@
 	/* cat-blob SP <object> LF */
 	p = command_buf.buf + strlen("cat-blob ");
 	if (*p == ':') {
-		char *x;
-		oe = find_mark(strtoumax(p + 1, &x, 10));
-		if (x == p + 1)
-			die("Invalid mark: %s", command_buf.buf);
+		oe = find_mark(parse_mark_ref_eol(p));
 		if (!oe)
 			die("Unknown mark: %s", command_buf.buf);
-		if (*x)
-			die("Garbage after mark: %s", command_buf.buf);
 		hashcpy(sha1, oe->idx.sha1);
 	} else {
 		if (get_sha1_hex(p, sha1))
-			die("Invalid SHA1: %s", command_buf.buf);
+			die("Invalid dataref: %s", command_buf.buf);
 		if (p[40])
 			die("Garbage after SHA1: %s", command_buf.buf);
 		oe = find_object(sha1);
@@ -2944,17 +2992,13 @@
 	struct object_entry *e;
 
 	if (**p == ':') {	/* <mark> */
-		char *endptr;
-		e = find_mark(strtoumax(*p + 1, &endptr, 10));
-		if (endptr == *p + 1)
-			die("Invalid mark: %s", command_buf.buf);
+		e = find_mark(parse_mark_ref_space(p));
 		if (!e)
 			die("Unknown mark: %s", command_buf.buf);
-		*p = endptr;
 		hashcpy(sha1, e->idx.sha1);
 	} else {	/* <sha1> */
 		if (get_sha1_hex(*p, sha1))
-			die("Invalid SHA1: %s", command_buf.buf);
+			die("Invalid dataref: %s", command_buf.buf);
 		e = find_object(sha1);
 		*p += 40;
 	}
diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index 0f5b5e5..924c884 100755
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -2635,4 +2635,291 @@
 	'n=$(grep $a verify | wc -l) &&
 	 test 1 = $n'
 
+###
+### series S
+###
+#
+# Make sure missing spaces and EOLs after mark references
+# cause errors.
+#
+# Setup:
+#
+#   1--2--4
+#    \   /
+#     -3-
+#
+#   commit marks:  301, 302, 303, 304
+#   blob marks:              403, 404, resp.
+#   note mark:          202
+#
+# The error message when a space is missing not at the
+# end of the line is:
+#
+#   Missing space after ..
+#
+# or when extra characters come after the mark at the end
+# of the line:
+#
+#   Garbage after ..
+#
+# or when the dataref is neither "inline " or a known SHA1,
+#
+#   Invalid dataref ..
+#
+test_tick
+
+cat >input <<INPUT_END
+commit refs/heads/S
+mark :301
+committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+data <<COMMIT
+commit 1
+COMMIT
+M 100644 inline hello.c
+data <<BLOB
+blob 1
+BLOB
+
+commit refs/heads/S
+mark :302
+committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+data <<COMMIT
+commit 2
+COMMIT
+from :301
+M 100644 inline hello.c
+data <<BLOB
+blob 2
+BLOB
+
+blob
+mark :403
+data <<BLOB
+blob 3
+BLOB
+
+blob
+mark :202
+data <<BLOB
+note 2
+BLOB
+INPUT_END
+
+test_expect_success 'S: initialize for S tests' '
+	git fast-import --export-marks=marks <input
+'
+
+#
+# filemodify, three datarefs
+#
+test_expect_success 'S: filemodify with garbage after mark must fail' '
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	commit refs/heads/S
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	commit N
+	COMMIT
+	M 100644 :403x hello.c
+	EOF
+	cat err &&
+	test_i18ngrep "space after mark" err
+'
+
+# inline is misspelled; fast-import thinks it is some unknown dataref
+test_expect_success 'S: filemodify with garbage after inline must fail' '
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	commit refs/heads/S
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	commit N
+	COMMIT
+	M 100644 inlineX hello.c
+	data <<BLOB
+	inline
+	BLOB
+	EOF
+	cat err &&
+	test_i18ngrep "nvalid dataref" err
+'
+
+test_expect_success 'S: filemodify with garbage after sha1 must fail' '
+	sha1=$(grep :403 marks | cut -d\  -f2) &&
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	commit refs/heads/S
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	commit N
+	COMMIT
+	M 100644 ${sha1}x hello.c
+	EOF
+	cat err &&
+	test_i18ngrep "space after SHA1" err
+'
+
+#
+# notemodify, three ways to say dataref
+#
+test_expect_success 'S: notemodify with garabge after mark dataref must fail' '
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	commit refs/heads/S
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	commit S note dataref markref
+	COMMIT
+	N :202x :302
+	EOF
+	cat err &&
+	test_i18ngrep "space after mark" err
+'
+
+test_expect_success 'S: notemodify with garbage after inline dataref must fail' '
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	commit refs/heads/S
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	commit S note dataref inline
+	COMMIT
+	N inlineX :302
+	data <<BLOB
+	note blob
+	BLOB
+	EOF
+	cat err &&
+	test_i18ngrep "nvalid dataref" err
+'
+
+test_expect_success 'S: notemodify with garbage after sha1 dataref must fail' '
+	sha1=$(grep :202 marks | cut -d\  -f2) &&
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	commit refs/heads/S
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	commit S note dataref sha1
+	COMMIT
+	N ${sha1}x :302
+	EOF
+	cat err &&
+	test_i18ngrep "space after SHA1" err
+'
+
+#
+# notemodify, mark in committish
+#
+test_expect_success 'S: notemodify with garbarge after mark committish must fail' '
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	commit refs/heads/Snotes
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	commit S note committish
+	COMMIT
+	N :202 :302x
+	EOF
+	cat err &&
+	test_i18ngrep "after mark" err
+'
+
+#
+# from
+#
+test_expect_success 'S: from with garbage after mark must fail' '
+	# no &&
+	git fast-import --import-marks=marks --export-marks=marks <<-EOF 2>err
+	commit refs/heads/S2
+	mark :303
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	commit 3
+	COMMIT
+	from :301x
+	M 100644 :403 hello.c
+	EOF
+
+	ret=$? &&
+	echo returned $ret &&
+	test $ret -ne 0 && # failed, but it created the commit
+
+	# go create the commit, need it for merge test
+	git fast-import --import-marks=marks --export-marks=marks <<-EOF &&
+	commit refs/heads/S2
+	mark :303
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	commit 3
+	COMMIT
+	from :301
+	M 100644 :403 hello.c
+	EOF
+
+	# now evaluate the error
+	cat err &&
+	test_i18ngrep "after mark" err
+'
+
+
+#
+# merge
+#
+test_expect_success 'S: merge with garbage after mark must fail' '
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	commit refs/heads/S
+	mark :304
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	merge 4
+	COMMIT
+	from :302
+	merge :303x
+	M 100644 :403 hello.c
+	EOF
+	cat err &&
+	test_i18ngrep "after mark" err
+'
+
+#
+# tag, from markref
+#
+test_expect_success 'S: tag with garbage after mark must fail' '
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	tag refs/tags/Stag
+	from :302x
+	tagger $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<TAG
+	tag S
+	TAG
+	EOF
+	cat err &&
+	test_i18ngrep "after mark" err
+'
+
+#
+# cat-blob markref
+#
+test_expect_success 'S: cat-blob with garbage after mark must fail' '
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	cat-blob :403x
+	EOF
+	cat err &&
+	test_i18ngrep "after mark" err
+'
+
+#
+# ls markref
+#
+test_expect_success 'S: ls with garbage after mark must fail' '
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	ls :302x hello.c
+	EOF
+	cat err &&
+	test_i18ngrep "space after mark" err
+'
+
+test_expect_success 'S: ls with garbage after sha1 must fail' '
+	sha1=$(grep :302 marks | cut -d\  -f2) &&
+	test_must_fail git fast-import --import-marks=marks <<-EOF 2>err &&
+	ls ${sha1}x hello.c
+	EOF
+	cat err &&
+	test_i18ngrep "space after tree-ish" err
+'
+
 test_done