diff --git a/assert/assertions.go b/assert/assertions.go
index a291b1fe6..eb800c1a9 100644
--- a/assert/assertions.go
+++ b/assert/assertions.go
@@ -1615,7 +1615,6 @@ func ErrorContains(t TestingT, theError error, contains string, msgAndArgs ...in
 
 // matchRegexp return true if a specified regexp matches a string.
 func matchRegexp(rx interface{}, str interface{}) bool {
-
 	var r *regexp.Regexp
 	if rr, ok := rx.(*regexp.Regexp); ok {
 		r = rr
@@ -1623,7 +1622,14 @@ func matchRegexp(rx interface{}, str interface{}) bool {
 		r = regexp.MustCompile(fmt.Sprint(rx))
 	}
 
-	return (r.FindStringIndex(fmt.Sprint(str)) != nil)
+	switch v := str.(type) {
+	case []byte:
+		return r.Match(v)
+	case string:
+		return r.MatchString(v)
+	default:
+		return r.MatchString(fmt.Sprint(v))
+	}
 
 }
 
diff --git a/assert/assertions_test.go b/assert/assertions_test.go
index 0ae36cd92..fa68fe210 100644
--- a/assert/assertions_test.go
+++ b/assert/assertions_test.go
@@ -1972,13 +1972,16 @@ func TestRegexp(t *testing.T) {
 	}{
 		{"^start", "start of the line"},
 		{"end$", "in the end"},
+		{"end$", "in the end"},
 		{"[0-9]{3}[.-]?[0-9]{2}[.-]?[0-9]{2}", "My phone number is 650.12.34"},
 	}
 
 	for _, tc := range cases {
 		True(t, Regexp(mockT, tc.rx, tc.str))
 		True(t, Regexp(mockT, regexp.MustCompile(tc.rx), tc.str))
+		True(t, Regexp(mockT, regexp.MustCompile(tc.rx), []byte(tc.str)))
 		False(t, NotRegexp(mockT, tc.rx, tc.str))
+		False(t, NotRegexp(mockT, tc.rx, []byte(tc.str)))
 		False(t, NotRegexp(mockT, regexp.MustCompile(tc.rx), tc.str))
 	}
 
@@ -1993,7 +1996,9 @@ func TestRegexp(t *testing.T) {
 	for _, tc := range cases {
 		False(t, Regexp(mockT, tc.rx, tc.str), "Expected \"%s\" to not match \"%s\"", tc.rx, tc.str)
 		False(t, Regexp(mockT, regexp.MustCompile(tc.rx), tc.str))
+		False(t, Regexp(mockT, regexp.MustCompile(tc.rx), []byte(tc.str)))
 		True(t, NotRegexp(mockT, tc.rx, tc.str))
+		True(t, NotRegexp(mockT, tc.rx, []byte(tc.str)))
 		True(t, NotRegexp(mockT, regexp.MustCompile(tc.rx), tc.str))
 	}
 }