diff --git a/helper/schema/schema.go b/helper/schema/schema.go
index d8b4e8166..d781da282 100644
--- a/helper/schema/schema.go
+++ b/helper/schema/schema.go
@@ -810,13 +810,14 @@ func (m schemaMap) diffString(
 		originalN = n
 		n = schema.StateFunc(n)
 	}
-	if n == nil {
-		n = schema.Type.Zero()
+	nraw := n
+	if nraw == nil {
+		nraw = schema.Type.Zero()
 	}
 	if err := mapstructure.WeakDecode(o, &os); err != nil {
 		return fmt.Errorf("%s: %s", k, err)
 	}
-	if err := mapstructure.WeakDecode(n, &ns); err != nil {
+	if err := mapstructure.WeakDecode(nraw, &ns); err != nil {
 		return fmt.Errorf("%s: %s", k, err)
 	}
 
diff --git a/helper/schema/schema_test.go b/helper/schema/schema_test.go
index bb32374f3..8f6119490 100644
--- a/helper/schema/schema_test.go
+++ b/helper/schema/schema_test.go
@@ -2009,6 +2009,29 @@ func TestSchemaMap_Diff(t *testing.T) {
 
 			Err: false,
 		},
+
+		// #50 - A set computed element shouldn't cause a diff
+		{
+			Schema: map[string]*Schema{
+				"active": &Schema{
+					Type:     TypeBool,
+					Computed: true,
+					ForceNew: true,
+				},
+			},
+
+			State: &terraform.InstanceState{
+				Attributes: map[string]string{
+					"active": "true",
+				},
+			},
+
+			Config: map[string]interface{}{},
+
+			Diff: nil,
+
+			Err: false,
+		},
 	}
 
 	for i, tc := range cases {