diff --git a/pkg/labels/regexp.go b/pkg/labels/regexp.go
index 2c9f7616da..532a548062 100644
--- a/pkg/labels/regexp.go
+++ b/pkg/labels/regexp.go
@@ -24,10 +24,11 @@ const maxSetMatches = 256
 type FastRegexMatcher struct {
 	re *regexp.Regexp
 
-	setMatches []string
-	prefix     string
-	suffix     string
-	contains   string
+	setMatches    []string
+	stringMatcher StringMatcher
+	prefix        string
+	suffix        string
+	contains      string
 }
 
 func NewFastRegexMatcher(v string) (*FastRegexMatcher, error) {
@@ -42,8 +43,9 @@ func NewFastRegexMatcher(v string) (*FastRegexMatcher, error) {
 		return nil, err
 	}
 	m := &FastRegexMatcher{
-		re:         re,
-		setMatches: findSetMatches(parsed, ""),
+		re:            re,
+		setMatches:    findSetMatches(parsed, ""),
+		stringMatcher: stringMatcherFromRegexp(parsed),
 	}
 
 	if parsed.Op == syntax.OpConcat {
@@ -193,6 +195,9 @@ func (m *FastRegexMatcher) MatchString(s string) bool {
 		}
 		return false
 	}
+	if m.stringMatcher != nil {
+		return m.stringMatcher.Matches(s)
+	}
 	if m.prefix != "" && !strings.HasPrefix(s, m.prefix) {
 		return false
 	}
@@ -262,18 +267,17 @@ func stringMatcherFromRegexp(re *syntax.Regexp) StringMatcher {
 	clearCapture(re)
 	clearBeginEndText(re)
 	switch re.Op {
-	case syntax.OpStar:
+	case syntax.OpPlus, syntax.OpStar:
+		if re.Sub[0].Op != syntax.OpAnyChar && re.Sub[0].Op != syntax.OpAnyCharNotNL {
+			return nil
+		}
 		return anyStringMatcher{
-			allowEmpty: true,
-			matchNL:    re.Flags&syntax.DotNL != 0,
+			allowEmpty: re.Op == syntax.OpStar,
+			matchNL:    re.Sub[0].Op == syntax.OpAnyChar,
 		}
 	case syntax.OpEmptyMatch:
 		return emptyStringMatcher{}
-	case syntax.OpPlus:
-		return anyStringMatcher{
-			allowEmpty: false,
-			matchNL:    re.Flags&syntax.DotNL != 0,
-		}
+
 	case syntax.OpLiteral:
 		return equalStringMatcher{
 			s:             string(re.Rune),
@@ -328,9 +332,9 @@ func stringMatcherFromRegexp(re *syntax.Regexp) StringMatcher {
 		}
 		if len(matches) > 0 {
 			return containsStringMatcher{
-				substr: matches,
-				left:   left,
-				right:  right,
+				substrings: matches,
+				left:       left,
+				right:      right,
 			}
 		}
 	}
@@ -338,32 +342,32 @@ func stringMatcherFromRegexp(re *syntax.Regexp) StringMatcher {
 }
 
 type containsStringMatcher struct {
-	substr []string
-	left   StringMatcher
-	right  StringMatcher
+	substrings []string
+	left       StringMatcher
+	right      StringMatcher
 }
 
 func (m containsStringMatcher) Matches(s string) bool {
 	var pos int
-	for _, substr := range m.substr {
+	for _, substr := range m.substrings {
 		pos = strings.Index(s, substr)
 		if pos < 0 {
 			continue
 		}
 		if m.right != nil && m.left != nil {
-			if m.left.Matches(s[:pos]) && m.right.Matches(s[pos+len(m.substr):]) {
+			if m.left.Matches(s[:pos]) && m.right.Matches(s[pos+len(substr):]) {
 				return true
 			}
 			continue
 		}
 		if m.left != nil {
-			if m.left.Matches(s[:pos]) {
+			if pos+len(substr) == len(s) && m.left.Matches(s[:pos]) {
 				return true
 			}
 			continue
 		}
 		if m.right != nil {
-			if m.right.Matches(s[pos+len(m.substr):]) {
+			if pos == 0 && m.right.Matches(s[pos+len(substr):]) {
 				return true
 			}
 			continue
@@ -395,7 +399,7 @@ type equalStringMatcher struct {
 }
 
 func (m equalStringMatcher) Matches(s string) bool {
-	if !m.caseSensitive {
+	if m.caseSensitive {
 		return m.s == s
 	}
 	return strings.EqualFold(m.s, s)
diff --git a/pkg/labels/regexp_test.go b/pkg/labels/regexp_test.go
index 4510f1694b..0380fff388 100644
--- a/pkg/labels/regexp_test.go
+++ b/pkg/labels/regexp_test.go
@@ -48,14 +48,17 @@ var (
 		"(?s:.*)",
 		"(?s:.+)",
 		"(?s:^.*foo$)",
+		"^(?i:foo|oo)|(bar)$",
 		"((.*)(bar|b|buzz)(.+)|foo)$",
 		"^$",
 		"(prometheus|api_prom)_api_v1_.+",
 		"10\\.0\\.(1|2)\\.+",
+		"10\\.0\\.(1|2).+",
+		"((fo(bar))|.+foo)",
 	}
 	values = []string{
 		"foo", " foo bar", "bar", "buzz\nbar", "bar foo", "bfoo", "\n", "\nfoo", "foo\n", "hello foo world", "hello foo\n world", "",
-		"\nfoo\n", strings.Repeat("f", 20), "prometheus", "prometheus_api_v1", "prometheus_api_v1_foo",
+		"FOO", "Foo", "OO", "Oo", "\nfoo\n", strings.Repeat("f", 20), "prometheus", "prometheus_api_v1", "prometheus_api_v1_foo",
 		"10.0.1.20", "10.0.2.10", "10.0.3.30", "10.0.4.40",
 	}
 )
@@ -203,6 +206,7 @@ func Test_OptimizeRegex(t *testing.T) {
 		exp     StringMatcher
 	}{
 		{".*", anyStringMatcher{allowEmpty: true, matchNL: false}},
+		{".*?", anyStringMatcher{allowEmpty: true, matchNL: false}},
 		{"(?s:.*)", anyStringMatcher{allowEmpty: true, matchNL: true}},
 		{"(.*)", anyStringMatcher{allowEmpty: true, matchNL: false}},
 		{"^.*$", anyStringMatcher{allowEmpty: true, matchNL: false}},
@@ -216,22 +220,23 @@ func Test_OptimizeRegex(t *testing.T) {
 		{"^(?i:foo)$", equalStringMatcher{s: "FOO", caseSensitive: false}},
 		{"^(?i:foo)|(bar)$", orStringMatcher([]StringMatcher{equalStringMatcher{s: "FOO", caseSensitive: false}, equalStringMatcher{s: "bar", caseSensitive: true}})},
 		{"^(?i:foo|oo)|(bar)$", orStringMatcher([]StringMatcher{orStringMatcher([]StringMatcher{equalStringMatcher{s: "FOO", caseSensitive: false}, equalStringMatcher{s: "OO", caseSensitive: false}}), equalStringMatcher{s: "bar", caseSensitive: true}})},
-		{".*foo.*", containsStringMatcher{substr: []string{"foo"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
-		{"(.*)foo.*", containsStringMatcher{substr: []string{"foo"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
-		{"(.*)foo(.*)", containsStringMatcher{substr: []string{"foo"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
-		{"(.+)foo(.*)", containsStringMatcher{substr: []string{"foo"}, left: anyStringMatcher{allowEmpty: false, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
-		{"^.+foo.+", containsStringMatcher{substr: []string{"foo"}, left: anyStringMatcher{allowEmpty: false, matchNL: false}, right: anyStringMatcher{allowEmpty: false, matchNL: false}}},
-		{"^(.*)(foo)(.*)$", containsStringMatcher{substr: []string{"foo"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
-		{"^(.*)(foo|foobar)(.*)$", containsStringMatcher{substr: []string{"foo", "foobar"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
-		{"^(.*)(foo|foobar)(.+)$", containsStringMatcher{substr: []string{"foo", "foobar"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: false, matchNL: false}}},
-		{"^(.*)(bar|b|buzz)(.+)$", containsStringMatcher{substr: []string{"bar", "b", "buzz"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: false, matchNL: false}}},
-		{"10\\.0\\.(1|2)\\.+", containsStringMatcher{substr: []string{"10.0.1", "10.0.2"}, left: nil, right: anyStringMatcher{allowEmpty: false, matchNL: false}}},
-		{"^.+foo", containsStringMatcher{substr: []string{"foo"}, left: anyStringMatcher{allowEmpty: false, matchNL: false}, right: nil}},
-		{"foo-.*$", containsStringMatcher{substr: []string{"foo-"}, left: nil, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
-		{"(prometheus|api_prom)_api_v1_.+", containsStringMatcher{substr: []string{"prometheus_api_v1_", "api_prom_api_v1_"}, left: nil, right: anyStringMatcher{allowEmpty: false, matchNL: false}}},
-		{"^((.*)(bar|b|buzz)(.+)|foo)$", orStringMatcher([]StringMatcher{containsStringMatcher{substr: []string{"bar", "b", "buzz"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: false, matchNL: false}}, equalStringMatcher{s: "foo", caseSensitive: true}})},
-		{"((fo(bar))|.+foo)", orStringMatcher([]StringMatcher{orStringMatcher([]StringMatcher{equalStringMatcher{s: "fobar", caseSensitive: true}}), containsStringMatcher{substr: []string{"foo"}, left: anyStringMatcher{allowEmpty: false, matchNL: false}, right: nil}})},
-		{"(.+)/(gateway|cortex-gw|cortex-gw-internal)", containsStringMatcher{substr: []string{"/gateway", "/cortex-gw", "/cortex-gw-internal"}, left: anyStringMatcher{allowEmpty: false, matchNL: false}, right: nil}},
+		{".*foo.*", containsStringMatcher{substrings: []string{"foo"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
+		{"(.*)foo.*", containsStringMatcher{substrings: []string{"foo"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
+		{"(.*)foo(.*)", containsStringMatcher{substrings: []string{"foo"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
+		{"(.+)foo(.*)", containsStringMatcher{substrings: []string{"foo"}, left: anyStringMatcher{allowEmpty: false, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
+		{"^.+foo.+", containsStringMatcher{substrings: []string{"foo"}, left: anyStringMatcher{allowEmpty: false, matchNL: false}, right: anyStringMatcher{allowEmpty: false, matchNL: false}}},
+		{"^(.*)(foo)(.*)$", containsStringMatcher{substrings: []string{"foo"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
+		{"^(.*)(foo|foobar)(.*)$", containsStringMatcher{substrings: []string{"foo", "foobar"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
+		{"^(.*)(foo|foobar)(.+)$", containsStringMatcher{substrings: []string{"foo", "foobar"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: false, matchNL: false}}},
+		{"^(.*)(bar|b|buzz)(.+)$", containsStringMatcher{substrings: []string{"bar", "b", "buzz"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: false, matchNL: false}}},
+		{"10\\.0\\.(1|2)\\.+", nil},
+		{"10\\.0\\.(1|2).+", containsStringMatcher{substrings: []string{"10.0.1", "10.0.2"}, left: nil, right: anyStringMatcher{allowEmpty: false, matchNL: false}}},
+		{"^.+foo", containsStringMatcher{substrings: []string{"foo"}, left: anyStringMatcher{allowEmpty: false, matchNL: false}, right: nil}},
+		{"foo-.*$", containsStringMatcher{substrings: []string{"foo-"}, left: nil, right: anyStringMatcher{allowEmpty: true, matchNL: false}}},
+		{"(prometheus|api_prom)_api_v1_.+", containsStringMatcher{substrings: []string{"prometheus_api_v1_", "api_prom_api_v1_"}, left: nil, right: anyStringMatcher{allowEmpty: false, matchNL: false}}},
+		{"^((.*)(bar|b|buzz)(.+)|foo)$", orStringMatcher([]StringMatcher{containsStringMatcher{substrings: []string{"bar", "b", "buzz"}, left: anyStringMatcher{allowEmpty: true, matchNL: false}, right: anyStringMatcher{allowEmpty: false, matchNL: false}}, equalStringMatcher{s: "foo", caseSensitive: true}})},
+		{"((fo(bar))|.+foo)", orStringMatcher([]StringMatcher{orStringMatcher([]StringMatcher{equalStringMatcher{s: "fobar", caseSensitive: true}}), containsStringMatcher{substrings: []string{"foo"}, left: anyStringMatcher{allowEmpty: false, matchNL: false}, right: nil}})},
+		{"(.+)/(gateway|cortex-gw|cortex-gw-internal)", containsStringMatcher{substrings: []string{"/gateway", "/cortex-gw", "/cortex-gw-internal"}, left: anyStringMatcher{allowEmpty: false, matchNL: false}, right: nil}},
 		// we don't support case insensitive matching for contains.
 		// This is because there's no strings.IndexOfFold function.
 		// We can revisit later if this is really popular by using strings.ToUpper.