diff --git a/builtin-grep.c b/builtin-grep.c
index 1df25b07b5..d79a6260a4 100644
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -367,7 +367,7 @@ static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 		push_arg("-h");
 	if (opt->regflags & REG_EXTENDED)
 		push_arg("-E");
-	if (opt->regflags & REG_ICASE)
+	if (opt->ignore_case)
 		push_arg("-i");
 	if (opt->binary == GREP_BINARY_NOMATCH)
 		push_arg("-I");
@@ -706,8 +706,8 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 		OPT_GROUP(""),
 		OPT_BOOLEAN('v', "invert-match", &opt.invert,
 			"show non-matching lines"),
-		OPT_BIT('i', "ignore-case", &opt.regflags,
-			"case insensitive matching", REG_ICASE),
+		OPT_BOOLEAN('i', "ignore-case", &opt.ignore_case,
+			"case insensitive matching"),
 		OPT_BOOLEAN('w', "word-regexp", &opt.word_regexp,
 			"match patterns only at word boundaries"),
 		OPT_SET_INT('a', "text", &opt.binary,
@@ -830,6 +830,8 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 		external_grep_allowed = 0;
 	if (!opt.pattern_list)
 		die("no pattern given.");
+	if (!opt.fixed && opt.ignore_case)
+		opt.regflags |= REG_ICASE;
 	if ((opt.regflags != REG_NEWLINE) && opt.fixed)
 		die("cannot mix --fixed-strings and regexp");
 	compile_grep_patterns(&opt);
diff --git a/grep.c b/grep.c
index 5d162dae6e..bdadf2c0cc 100644
--- a/grep.c
+++ b/grep.c
@@ -41,6 +41,7 @@ static void compile_regexp(struct grep_pat *p, struct grep_opt *opt)
 	int err;
 
 	p->word_regexp = opt->word_regexp;
+	p->ignore_case = opt->ignore_case;
 
 	if (opt->fixed || is_fixed(p->pattern))
 		p->fixed = 1;
@@ -262,9 +263,15 @@ static void show_name(struct grep_opt *opt, const char *name)
 	printf("%s%c", name, opt->null_following_name ? '\0' : '\n');
 }
 
-static int fixmatch(const char *pattern, char *line, regmatch_t *match)
+
+static int fixmatch(const char *pattern, char *line, int ignore_case, regmatch_t *match)
 {
-	char *hit = strstr(line, pattern);
+	char *hit;
+	if (ignore_case)
+		hit = strcasestr(line, pattern);
+	else
+		hit = strstr(line, pattern);
+
 	if (!hit) {
 		match->rm_so = match->rm_eo = -1;
 		return REG_NOMATCH;
@@ -326,7 +333,7 @@ static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,
 
  again:
 	if (p->fixed)
-		hit = !fixmatch(p->pattern, bol, pmatch);
+		hit = !fixmatch(p->pattern, bol, p->ignore_case, pmatch);
 	else
 		hit = !regexec(&p->regexp, bol, 1, pmatch, eflags);
 
diff --git a/grep.h b/grep.h
index f6eecc62c0..75370f60d7 100644
--- a/grep.h
+++ b/grep.h
@@ -32,6 +32,7 @@ struct grep_pat {
 	enum grep_header_field field;
 	regex_t regexp;
 	unsigned fixed:1;
+	unsigned ignore_case:1;
 	unsigned word_regexp:1;
 };
 
@@ -64,6 +65,7 @@ struct grep_opt {
 	regex_t regexp;
 	int linenum;
 	int invert;
+	int ignore_case;
 	int status_only;
 	int name_only;
 	int unmatch_name_only;
diff --git a/t/t7002-grep.sh b/t/t7002-grep.sh
index ae5290ab43..3a103fec96 100755
--- a/t/t7002-grep.sh
+++ b/t/t7002-grep.sh
@@ -14,6 +14,7 @@ int main(int argc, const char **argv)
 {
 	printf("Hello world.\n");
 	return 0;
+	/* char ?? */
 }
 EOF
 
@@ -411,4 +412,13 @@ test_expect_success 'grep from a subdirectory to search wider area (2)' '
 	)
 '
 
+cat >expected <<EOF
+hello.c:int main(int argc, const char **argv)
+EOF
+
+test_expect_success 'grep -Fi' '
+	git grep -Fi "CHAR *" >actual &&
+	test_cmp expected actual
+'
+
 test_done