diff --git a/builtin/blame.c b/builtin/blame.c
index 86100e9662..77707819af 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -1375,10 +1375,15 @@ static void get_ac_line(const char *inbuf, const char *what,
 	maillen = ident.mail_end - ident.mail_begin;
 	mailbuf = ident.mail_begin;
 
-	*time = strtoul(ident.date_begin, NULL, 10);
+	if (ident.date_begin && ident.date_end)
+		*time = strtoul(ident.date_begin, NULL, 10);
+	else
+		*time = 0;
 
-	len = ident.tz_end - ident.tz_begin;
-	strbuf_add(tz, ident.tz_begin, len);
+	if (ident.tz_begin && ident.tz_end)
+		strbuf_add(tz, ident.tz_begin, ident.tz_end - ident.tz_begin);
+	else
+		strbuf_addstr(tz, "(unknown)");
 
 	/*
 	 * Now, convert both name and e-mail using mailmap
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 40f87b4649..045cee7bce 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -16,73 +16,6 @@
 #define BATCH 1
 #define BATCH_CHECK 2
 
-static void pprint_tag(const unsigned char *sha1, const char *buf, unsigned long size)
-{
-	/* the parser in tag.c is useless here. */
-	const char *endp = buf + size;
-	const char *cp = buf;
-
-	while (cp < endp) {
-		char c = *cp++;
-		if (c != '\n')
-			continue;
-		if (7 <= endp - cp && !memcmp("tagger ", cp, 7)) {
-			const char *tagger = cp;
-
-			/* Found the tagger line.  Copy out the contents
-			 * of the buffer so far.
-			 */
-			write_or_die(1, buf, cp - buf);
-
-			/*
-			 * Do something intelligent, like pretty-printing
-			 * the date.
-			 */
-			while (cp < endp) {
-				if (*cp++ == '\n') {
-					/* tagger to cp is a line
-					 * that has ident and time.
-					 */
-					const char *sp = tagger;
-					char *ep;
-					unsigned long date;
-					long tz;
-					while (sp < cp && *sp != '>')
-						sp++;
-					if (sp == cp) {
-						/* give up */
-						write_or_die(1, tagger,
-							     cp - tagger);
-						break;
-					}
-					while (sp < cp &&
-					       !('0' <= *sp && *sp <= '9'))
-						sp++;
-					write_or_die(1, tagger, sp - tagger);
-					date = strtoul(sp, &ep, 10);
-					tz = strtol(ep, NULL, 10);
-					sp = show_date(date, tz, 0);
-					write_or_die(1, sp, strlen(sp));
-					xwrite(1, "\n", 1);
-					break;
-				}
-			}
-			break;
-		}
-		if (cp < endp && *cp == '\n')
-			/* end of header */
-			break;
-	}
-	/* At this point, we have copied out the header up to the end of
-	 * the tagger line and cp points at one past \n.  It could be the
-	 * next header line after the tagger line, or it could be another
-	 * \n that marks the end of the headers.  We need to copy out the
-	 * remainder as is.
-	 */
-	if (cp < endp)
-		write_or_die(1, cp, endp - cp);
-}
-
 static int cat_one_file(int opt, const char *exp_type, const char *obj_name)
 {
 	unsigned char sha1[20];
@@ -133,10 +66,6 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name)
 		buf = read_sha1_file(sha1, &type, &size);
 		if (!buf)
 			die("Cannot read object %s", obj_name);
-		if (type == OBJ_TAG) {
-			pprint_tag(sha1, buf, size);
-			return 0;
-		}
 
 		/* otherwise just spit out the data */
 		break;
diff --git a/pretty.c b/pretty.c
index d3a82d22d3..c11624832b 100644
--- a/pretty.c
+++ b/pretty.c
@@ -393,6 +393,19 @@ static void add_rfc2047(struct strbuf *sb, const char *line, size_t len,
 	strbuf_addstr(sb, "?=");
 }
 
+static const char *show_ident_date(const struct ident_split *ident,
+				   enum date_mode mode)
+{
+	unsigned long date = 0;
+	int tz = 0;
+
+	if (ident->date_begin && ident->date_end)
+		date = strtoul(ident->date_begin, NULL, 10);
+	if (ident->tz_begin && ident->tz_end)
+		tz = strtol(ident->tz_begin, NULL, 10);
+	return show_date(date, tz, mode);
+}
+
 void pp_user_info(const struct pretty_print_context *pp,
 		  const char *what, struct strbuf *sb,
 		  const char *line, const char *encoding)
@@ -401,12 +414,10 @@ void pp_user_info(const struct pretty_print_context *pp,
 	struct strbuf mail;
 	struct ident_split ident;
 	int linelen;
-	char *line_end, *date;
+	char *line_end;
 	const char *mailbuf, *namebuf;
 	size_t namelen, maillen;
 	int max_length = 78; /* per rfc2822 */
-	unsigned long time;
-	int tz;
 
 	if (pp->fmt == CMIT_FMT_ONELINE)
 		return;
@@ -438,8 +449,6 @@ void pp_user_info(const struct pretty_print_context *pp,
 	strbuf_add(&name, namebuf, namelen);
 
 	namelen = name.len + mail.len + 3; /* ' ' + '<' + '>' */
-	time = strtoul(ident.date_begin, &date, 10);
-	tz = strtol(date, NULL, 10);
 
 	if (pp->fmt == CMIT_FMT_EMAIL) {
 		strbuf_addstr(sb, "From: ");
@@ -472,13 +481,16 @@ void pp_user_info(const struct pretty_print_context *pp,
 
 	switch (pp->fmt) {
 	case CMIT_FMT_MEDIUM:
-		strbuf_addf(sb, "Date:   %s\n", show_date(time, tz, pp->date_mode));
+		strbuf_addf(sb, "Date:   %s\n",
+			    show_ident_date(&ident, pp->date_mode));
 		break;
 	case CMIT_FMT_EMAIL:
-		strbuf_addf(sb, "Date: %s\n", show_date(time, tz, DATE_RFC2822));
+		strbuf_addf(sb, "Date: %s\n",
+			    show_ident_date(&ident, DATE_RFC2822));
 		break;
 	case CMIT_FMT_FULLER:
-		strbuf_addf(sb, "%sDate: %s\n", what, show_date(time, tz, pp->date_mode));
+		strbuf_addf(sb, "%sDate: %s\n", what,
+			    show_ident_date(&ident, pp->date_mode));
 		break;
 	default:
 		/* notin' */
@@ -688,8 +700,6 @@ static size_t format_person_part(struct strbuf *sb, char part,
 {
 	/* currently all placeholders have same length */
 	const int placeholder_len = 2;
-	int tz;
-	unsigned long date = 0;
 	struct ident_split s;
 	const char *name, *mail;
 	size_t maillen, namelen;
@@ -716,30 +726,23 @@ static size_t format_person_part(struct strbuf *sb, char part,
 	if (!s.date_begin)
 		goto skip;
 
-	date = strtoul(s.date_begin, NULL, 10);
-
 	if (part == 't') {	/* date, UNIX timestamp */
 		strbuf_add(sb, s.date_begin, s.date_end - s.date_begin);
 		return placeholder_len;
 	}
 
-	/* parse tz */
-	tz = strtoul(s.tz_begin + 1, NULL, 10);
-	if (*s.tz_begin == '-')
-		tz = -tz;
-
 	switch (part) {
 	case 'd':	/* date */
-		strbuf_addstr(sb, show_date(date, tz, dmode));
+		strbuf_addstr(sb, show_ident_date(&s, dmode));
 		return placeholder_len;
 	case 'D':	/* date, RFC2822 style */
-		strbuf_addstr(sb, show_date(date, tz, DATE_RFC2822));
+		strbuf_addstr(sb, show_ident_date(&s, DATE_RFC2822));
 		return placeholder_len;
 	case 'r':	/* date, relative */
-		strbuf_addstr(sb, show_date(date, tz, DATE_RELATIVE));
+		strbuf_addstr(sb, show_ident_date(&s, DATE_RELATIVE));
 		return placeholder_len;
 	case 'i':	/* date, ISO 8601 */
-		strbuf_addstr(sb, show_date(date, tz, DATE_ISO8601));
+		strbuf_addstr(sb, show_ident_date(&s, DATE_ISO8601));
 		return placeholder_len;
 	}
 
diff --git a/t/t1006-cat-file.sh b/t/t1006-cat-file.sh
index 9820f70c84..9cc5c6bf4d 100755
--- a/t/t1006-cat-file.sh
+++ b/t/t1006-cat-file.sh
@@ -134,15 +134,12 @@ tagger $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>"
 tag_description="This is a tag"
 tag_content="$tag_header_without_timestamp 0000000000 +0000
 
-$tag_description"
-tag_pretty_content="$tag_header_without_timestamp Thu Jan 1 00:00:00 1970 +0000
-
 $tag_description"
 
 tag_sha1=$(echo_without_newline "$tag_content" | git mktag)
 tag_size=$(strlen "$tag_content")
 
-run_tests 'tag' $tag_sha1 $tag_size "$tag_content" "$tag_pretty_content" 1
+run_tests 'tag' $tag_sha1 $tag_size "$tag_content" "$tag_content" 1
 
 test_expect_success \
     "Reach a blob from a tag pointing to it" \
diff --git a/t/t4212-log-corrupt.sh b/t/t4212-log-corrupt.sh
new file mode 100755
index 0000000000..ec5099b83d
--- /dev/null
+++ b/t/t4212-log-corrupt.sh
@@ -0,0 +1,42 @@
+#!/bin/sh
+
+test_description='git log with invalid commit headers'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit foo &&
+
+	git cat-file commit HEAD |
+	sed "/^author /s/>/>-<>/" >broken_email.commit &&
+	git hash-object -w -t commit broken_email.commit >broken_email.hash &&
+	git update-ref refs/heads/broken_email $(cat broken_email.hash)
+'
+
+test_expect_success 'git log with broken author email' '
+	{
+		echo commit $(cat broken_email.hash)
+		echo "Author: A U Thor <author@example.com>"
+		echo "Date:   Thu Jan 1 00:00:00 1970 +0000"
+		echo
+		echo "    foo"
+	} >expect.out &&
+	: >expect.err &&
+
+	git log broken_email >actual.out 2>actual.err &&
+
+	test_cmp expect.out actual.out &&
+	test_cmp expect.err actual.err
+'
+
+test_expect_success 'git log --format with broken author email' '
+	echo "A U Thor+author@example.com+" >expect.out &&
+	: >expect.err &&
+
+	git log --format="%an+%ae+%ad" broken_email >actual.out 2>actual.err &&
+
+	test_cmp expect.out actual.out &&
+	test_cmp expect.err actual.err
+'
+
+test_done