diff --git a/assert/assertions.go b/assert/assertions.go
index 166f63726..6b19e061f 100644
--- a/assert/assertions.go
+++ b/assert/assertions.go
@@ -1526,6 +1526,9 @@ func InDeltaMapValues(t TestingT, expected, actual interface{}, delta float64, m
 	}
 
 	for _, k := range expectedMap.MapKeys() {
+		if !k.Type().AssignableTo(actualMap.Type().Key()) {
+			return Fail(t, fmt.Sprintf("Cannot compare map keys of type %v with %v", k.Type(), actualMap.Type().Key()), msgAndArgs...)
+		}
 		ev := expectedMap.MapIndex(k)
 		av := actualMap.MapIndex(k)
 
diff --git a/assert/assertions_test.go b/assert/assertions_test.go
index 11642e096..51148510f 100644
--- a/assert/assertions_test.go
+++ b/assert/assertions_test.go
@@ -2442,6 +2442,31 @@ func TestInDeltaMapValues(t *testing.T) {
 	}
 }
 
+func TestInDeltaMapValuesKeyTypes(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name     string
+		expected interface{}
+		actual   interface{}
+	}{
+		{"string and int", map[string]float64{"1": 1}, map[int]float64{1: 1}},
+		{"int and int64", map[int]float64{1: 1}, map[int64]float64{1: 1}},
+		{"interface and string", map[interface{}]float64{"key": 1}, map[string]float64{"key": 1}},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			out := &outputT{buf: bytes.NewBuffer(nil)}
+			NotPanics(t, func() {
+				False(t, InDeltaMapValues(out, tc.expected, tc.actual, 0.1, "map comparison"))
+			})
+			Contains(t, out.buf.String(), "map comparison")
+		})
+	}
+
+	// A concrete key can already be assigned to an interface-keyed map.
+	True(t, InDeltaMapValues(t, map[string]float64{"key": 1}, map[interface{}]float64{"key": 1.01}, 0.1))
+}
+
 func TestInEpsilon(t *testing.T) {
 	t.Parallel()