diff --git a/cty/function/stdlib/json.go b/cty/function/stdlib/json.go
index 07901c65..02770a65 100644
--- a/cty/function/stdlib/json.go
+++ b/cty/function/stdlib/json.go
@@ -12,6 +12,7 @@ var JSONEncodeFunc = function.New(&function.Spec{
 			Name:             "val",
 			Type:             cty.DynamicPseudoType,
 			AllowDynamicType: true,
+			AllowNull:        true,
 		},
 	},
 	Type: function.StaticReturnType(cty.String),
@@ -24,6 +25,10 @@ var JSONEncodeFunc = function.New(&function.Spec{
 			return cty.UnknownVal(retType), nil
 		}
 
+		if val.IsNull() {
+			return cty.StringVal("null"), nil
+		}
+
 		buf, err := json.Marshal(val, val.Type())
 		if err != nil {
 			return cty.NilVal, err
diff --git a/cty/function/stdlib/json_test.go b/cty/function/stdlib/json_test.go
index e67ba6e0..5c1348fc 100644
--- a/cty/function/stdlib/json_test.go
+++ b/cty/function/stdlib/json_test.go
@@ -52,6 +52,10 @@ func TestJSONEncode(t *testing.T) {
 			cty.DynamicVal,
 			cty.UnknownVal(cty.String),
 		},
+		{
+			cty.NullVal(cty.String),
+			cty.StringVal("null"),
+		},
 	}
 
 	for _, test := range tests {