diff --git a/pkg/strutil/strutil.go b/pkg/strutil/strutil.go
index 463dccba8..2039722b1 100644
--- a/pkg/strutil/strutil.go
+++ b/pkg/strutil/strutil.go
@@ -17,7 +17,11 @@ limitations under the License.
 // Package strutil contains string and byte processing functions.
 package strutil
 
-import "strings"
+import (
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
 
 // Fork of Go's implementation in pkg/strings/strings.go:
 // Generic split: splits after each instance of sep,
@@ -75,8 +79,28 @@ func HasSuffixFold(s, suffix string) bool {
 	return strings.EqualFold(s[len(s)-len(suffix):], suffix)
 }
 
-// ContainsFold is like strings.Contains but (ought to) use Unicode case-folding.
+// ContainsFold is like strings.Contains but uses Unicode case-folding.
 func ContainsFold(s, substr string) bool {
-	// TODO: Make this not do allocations.
-	return strings.Contains(strings.ToLower(s), strings.ToLower(substr))
+	if substr == "" {
+		return true
+	}
+	if s == "" {
+		return false
+	}
+	firstRune := rune(substr[0])
+	if firstRune >= utf8.RuneSelf {
+		firstRune, _ = utf8.DecodeRuneInString(substr)
+	}
+	firstLowerRune := unicode.SimpleFold(firstRune)
+	for i, rune := range s {
+		if len(s)-i < len(substr) {
+			return false
+		}
+		if rune == firstLowerRune || unicode.SimpleFold(rune) == firstLowerRune {
+			if HasPrefixFold(s[i:], substr) {
+				return true
+			}
+		}
+	}
+	return false
 }
diff --git a/pkg/strutil/strutil_test.go b/pkg/strutil/strutil_test.go
index 5acc81aa2..b35eebecd 100644
--- a/pkg/strutil/strutil_test.go
+++ b/pkg/strutil/strutil_test.go
@@ -95,3 +95,44 @@ func TestHasSuffixFold(t *testing.T) {
 		}
 	}
 }
+
+func TestContainsFold(t *testing.T) {
+	// TODO: more tests, more languages.
+	// The k,K,Kelvin (for now failing) example once TODO in HasPrefixFold is fixed.
+	tests := []struct {
+		s, substr string
+		result    bool
+	}{
+		{"camli", "CAML", true},
+		{"CAMLI", "caml", true},
+		{"cam", "Cam", true},
+		{"мир", "ми", true},
+		{"МИP", "ми", true},
+		{"КАМЛИЙСТОР", "камлийс", true},
+		{"КаМлИйСтОр", "КаМлИйС", true},
+		{"camli", "car", false},
+		{"caml", "camli", false},
+
+		{"camli", "AMLI", true},
+		{"CAMLI", "amli", true},
+		{"mli", "MLI", true},
+		{"мир", "ир", true},
+		{"МИP", "ми", true},
+		{"КАМЛИЙСТОР", "лийстор", true},
+		{"КаМлИйСтОр", "лИйСтОр", true},
+		{"мир", "р", true},
+		{"camli", "ali", false},
+		{"amli", "camli", false},
+
+		{"МИP", "и", true},
+		{"мир", "и", true},
+		{"КАМЛИЙСТОР", "лийс", true},
+		{"КаМлИйСтОр", "лИйС", true},
+	}
+	for _, tt := range tests {
+		r := ContainsFold(tt.s, tt.substr)
+		if r != tt.result {
+			t.Errorf("ContainsFold(%q, %q) returned %v", tt.s, tt.substr, r)
+		}
+	}
+}