diff --git a/src/index.js b/src/index.js
index 4545324..c67d25f 100644
--- a/src/index.js
+++ b/src/index.js
@@ -204,7 +204,7 @@ function toReadableString ( value, indent, replacer ) {
 	"indent": 4,
 	"truncate_views": 50,
     };
-    if ( typeof indent === "object" && indent !== null )
+    if ( is_object(indent) )
 	options				= Object.assign( options, indent );
     else if ( indent !== undefined )
 	options.indent			= indent;
@@ -218,8 +218,6 @@ function toReadableString ( value, indent, replacer ) {
 	    return `${RAW_PREFIX}[Circular reference to #/${seen.get(v).join('/')}]`;
 
 	if ( is_object(v) ) {
-	    seen.set( v, path ); // Add value before copy
-
 	    try {
 		v			= v.toJSON( k );
 	    } catch (err)  {
@@ -228,6 +226,8 @@ function toReadableString ( value, indent, replacer ) {
 			    || err.message.includes("Cannot read property 'toJSON'"))) )
 		    throw err;
 	    }
+	    if ( is_object(v) )
+		seen.set( v, path ); // Add value after toJSON but before copy
 
 	    if ( v.constructor.name === "Object" )
 		v			= Object.assign({}, v);
diff --git a/tests/unit/test_debug.js b/tests/unit/test_debug.js
index 5f7c316..905ed27 100644
--- a/tests/unit/test_debug.js
+++ b/tests/unit/test_debug.js
@@ -102,6 +102,28 @@ function basic_tests () {
 	    ).to.equal(`{"a":9007199254740991n,"b":9007199254740991n}`);
 	}
     });
+
+    it("should not circular reference primitive values", async () => {
+	class Something {
+	    toJSON () {
+		return "primitive value";
+	    }
+	}
+	const eventual_primitive	= new Something();
+
+	const input			= {
+	    "eventual_primitive": eventual_primitive,
+	    "sublevel": {
+		"list": [
+		    eventual_primitive,
+		],
+		"eventual_primitive": eventual_primitive,
+	    }
+	};
+	let text			= debug( input );
+
+	expect( text			).to.equal( JSON.stringify(input, null, 4) );
+    });
 }
 
 describe("Debug", () => {