diff --git a/assert/assertion_format.go b/assert/assertion_format.go
index a19a89279..6078db869 100644
--- a/assert/assertion_format.go
+++ b/assert/assertion_format.go
@@ -366,6 +366,8 @@ func InDeltaf(t TestingT, expected interface{}, actual interface{}, delta float6
 }
 
 // InDeltaMapValuesf is the same as InDelta, but it compares all values between two maps. Both maps must have exactly the same keys.
+// When the assertion fails for a particular key, the failure message is prefixed with key[<k>]:
+// so the offending entry can be identified at a glance.
 func InDeltaMapValuesf(t TestingT, expected interface{}, actual interface{}, delta float64, msg string, args ...interface{}) bool {
 	if h, ok := t.(tHelper); ok {
 		h.Helper()
diff --git a/assert/assertion_forward.go b/assert/assertion_forward.go
index cd2a86061..7d38786fe 100644
--- a/assert/assertion_forward.go
+++ b/assert/assertion_forward.go
@@ -713,6 +713,8 @@ func (a *Assertions) InDelta(expected interface{}, actual interface{}, delta flo
 }
 
 // InDeltaMapValues is the same as InDelta, but it compares all values between two maps. Both maps must have exactly the same keys.
+// When the assertion fails for a particular key, the failure message is prefixed with key[<k>]:
+// so the offending entry can be identified at a glance.
 func (a *Assertions) InDeltaMapValues(expected interface{}, actual interface{}, delta float64, msgAndArgs ...interface{}) bool {
 	if h, ok := a.t.(tHelper); ok {
 		h.Helper()
@@ -721,6 +723,8 @@ func (a *Assertions) InDeltaMapValues(expected interface{}, actual interface{},
 }
 
 // InDeltaMapValuesf is the same as InDelta, but it compares all values between two maps. Both maps must have exactly the same keys.
+// When the assertion fails for a particular key, the failure message is prefixed with key[<k>]:
+// so the offending entry can be identified at a glance.
 func (a *Assertions) InDeltaMapValuesf(expected interface{}, actual interface{}, delta float64, msg string, args ...interface{}) bool {
 	if h, ok := a.t.(tHelper); ok {
 		h.Helper()
diff --git a/assert/assertions.go b/assert/assertions.go
index 1419e4776..aa5551c27 100644
--- a/assert/assertions.go
+++ b/assert/assertions.go
@@ -1508,6 +1508,8 @@ func InDeltaSlice(t TestingT, expected, actual interface{}, delta float64, msgAn
 }
 
 // InDeltaMapValues is the same as InDelta, but it compares all values between two maps. Both maps must have exactly the same keys.
+// When the assertion fails for a particular key, the failure message is prefixed with key[<k>]:
+// so the offending entry can be identified at a glance.
 func InDeltaMapValues(t TestingT, expected, actual interface{}, delta float64, msgAndArgs ...interface{}) bool {
 	if h, ok := t.(tHelper); ok {
 		h.Helper()
@@ -1537,14 +1539,23 @@ func InDeltaMapValues(t TestingT, expected, actual interface{}, delta float64, m
 			return Fail(t, fmt.Sprintf("missing key %q in actual map", k), msgAndArgs...)
 		}
 
-		if !InDelta(
-			t,
-			ev.Interface(),
-			av.Interface(),
-			delta,
-			msgAndArgs...,
-		) {
-			return false
+		af, aok := toFloat(ev.Interface())
+		bf, bok := toFloat(av.Interface())
+		if !aok || !bok {
+			return Fail(t, fmt.Sprintf("key[%v]: Parameters must be numerical", k), msgAndArgs...)
+		}
+		if math.IsNaN(af) && math.IsNaN(bf) {
+			continue
+		}
+		if math.IsNaN(af) {
+			return Fail(t, fmt.Sprintf("key[%v]: Expected must not be NaN", k), msgAndArgs...)
+		}
+		if math.IsNaN(bf) {
+			return Fail(t, fmt.Sprintf("key[%v]: Expected %v with delta %v, but was NaN", k, ev.Interface(), delta), msgAndArgs...)
+		}
+		dt := af - bf
+		if dt < -delta || dt > delta {
+			return Fail(t, fmt.Sprintf("key[%v]: Max difference between %v and %v allowed is %v, but difference was %v", k, ev.Interface(), av.Interface(), delta, dt), msgAndArgs...)
 		}
 	}
 
diff --git a/assert/assertions_test.go b/assert/assertions_test.go
index 11642e096..a983c1307 100644
--- a/assert/assertions_test.go
+++ b/assert/assertions_test.go
@@ -2442,6 +2442,56 @@ func TestInDeltaMapValues(t *testing.T) {
 	}
 }
 
+func TestInDeltaMapValues_ErrorIncludesKey(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		title    string
+		expected interface{}
+		actual   interface{}
+		delta    float64
+		wantSub  string
+	}{
+		{
+			title:    "delta exceeded on string key",
+			expected: map[string]int{"a": 3, "b": 1},
+			actual:   map[string]int{"a": 4, "b": 1},
+			delta:    0.01,
+			wantSub:  "key[a]:",
+		},
+		{
+			title:    "delta exceeded on int key",
+			expected: map[int]float64{1: 1.0, 2: 2.0},
+			actual:   map[int]float64{1: 1.0, 2: 5.0},
+			delta:    0.1,
+			wantSub:  "key[2]:",
+		},
+		{
+			title:    "non-numerical value at key",
+			expected: map[string]interface{}{"a": "not-a-number"},
+			actual:   map[string]interface{}{"a": "still-not"},
+			delta:    0.1,
+			wantSub:  "key[a]: Parameters must be numerical",
+		},
+		{
+			title:    "actual is NaN",
+			expected: map[string]float64{"x": 1.0},
+			actual:   map[string]float64{"x": math.NaN()},
+			delta:    0.1,
+			wantSub:  "key[x]:",
+		},
+	} {
+		t.Run(tc.title, func(t *testing.T) {
+			mockT := new(mockTestingT)
+			False(t, InDeltaMapValues(mockT, tc.expected, tc.actual, tc.delta),
+				"InDeltaMapValues should fail for %s", tc.title)
+			True(t, mockT.Failed(), "mockT should have recorded a failure")
+			Contains(t, mockT.errorString(), tc.wantSub,
+				"failure message should mention the offending map key")
+		})
+	}
+}
+
 func TestInEpsilon(t *testing.T) {
 	t.Parallel()
 
diff --git a/require/require.go b/require/require.go
index 652871f2e..4a22263f7 100644
--- a/require/require.go
+++ b/require/require.go
@@ -867,6 +867,8 @@ func InDelta(t TestingT, expected interface{}, actual interface{}, delta float64
 }
 
 // InDeltaMapValues is the same as InDelta, but it compares all values between two maps. Both maps must have exactly the same keys.
+// When the assertion fails for a particular key, the failure message is prefixed with key[<k>]:
+// so the offending entry can be identified at a glance.
 func InDeltaMapValues(t TestingT, expected interface{}, actual interface{}, delta float64, msgAndArgs ...interface{}) {
 	if h, ok := t.(tHelper); ok {
 		h.Helper()
@@ -878,6 +880,8 @@ func InDeltaMapValues(t TestingT, expected interface{}, actual interface{}, delt
 }
 
 // InDeltaMapValuesf is the same as InDelta, but it compares all values between two maps. Both maps must have exactly the same keys.
+// When the assertion fails for a particular key, the failure message is prefixed with key[<k>]:
+// so the offending entry can be identified at a glance.
 func InDeltaMapValuesf(t TestingT, expected interface{}, actual interface{}, delta float64, msg string, args ...interface{}) {
 	if h, ok := t.(tHelper); ok {
 		h.Helper()
diff --git a/require/require_forward.go b/require/require_forward.go
index edac147ef..861d76380 100644
--- a/require/require_forward.go
+++ b/require/require_forward.go
@@ -690,6 +690,8 @@ func (a *Assertions) InDelta(expected interface{}, actual interface{}, delta flo
 }
 
 // InDeltaMapValues is the same as InDelta, but it compares all values between two maps. Both maps must have exactly the same keys.
+// When the assertion fails for a particular key, the failure message is prefixed with key[<k>]:
+// so the offending entry can be identified at a glance.
 func (a *Assertions) InDeltaMapValues(expected interface{}, actual interface{}, delta float64, msgAndArgs ...interface{}) {
 	if h, ok := a.t.(tHelper); ok {
 		h.Helper()
@@ -698,6 +700,8 @@ func (a *Assertions) InDeltaMapValues(expected interface{}, actual interface{},
 }
 
 // InDeltaMapValuesf is the same as InDelta, but it compares all values between two maps. Both maps must have exactly the same keys.
+// When the assertion fails for a particular key, the failure message is prefixed with key[<k>]:
+// so the offending entry can be identified at a glance.
 func (a *Assertions) InDeltaMapValuesf(expected interface{}, actual interface{}, delta float64, msg string, args ...interface{}) {
 	if h, ok := a.t.(tHelper); ok {
 		h.Helper()