diff --git a/spec/core/PrettyPrintSpec.js b/spec/core/PrettyPrintSpec.js
index 47a5758a..64dea0fd 100644
--- a/spec/core/PrettyPrintSpec.js
+++ b/spec/core/PrettyPrintSpec.js
@@ -333,4 +333,27 @@ describe("jasmineUnderTest.pp", function () {
 
     expect(jasmineUnderTest.pp(obj)).toEqual("null({ foo: 'bar' })");
   });
+
+  it("should gracefully handle objects with invalid toString implementations", function () {
+    var obj = {
+      foo: {
+        toString: function() {
+          // Invalid: toString returning a number
+          return 3;
+        }
+      },
+      bar: {
+        toString: function() {
+          // Invalid: toString returning an object
+          return new Error("bar");
+        }
+      },
+      // Valid: an actual number
+      baz: 3,
+      // Valid: an actual Error object
+      qux: new Error("bar")
+    };
+
+    expect(jasmineUnderTest.pp(obj)).toEqual("Object({ foo: [object Number], bar: [object Error], baz: 3, qux: Error: bar })");
+  });
 });
diff --git a/src/core/PrettyPrinter.js b/src/core/PrettyPrinter.js
index cb738d28..42b89784 100644
--- a/src/core/PrettyPrinter.js
+++ b/src/core/PrettyPrinter.js
@@ -266,6 +266,12 @@ getJasmineRequireObj().pp = function(j$) {
   };
 
   PrettyPrinter.prototype.append = function(value) {
+    // This check protects us from the rare case where an object has overriden
+    // `toString()` with an invalid implementation (returning a non-string).
+    if (typeof value !== 'string') {
+      value = Object.prototype.toString.call(value);
+    }
+
     var result = truncate(value, j$.MAX_PRETTY_PRINT_CHARS - this.length);
     this.length += result.value.length;
     this.stringParts.push(result.value);