diff --git a/progtest/src/TestRunner.js b/progtest/src/TestRunner.js
index 92690187..d24f38f2 100644
--- a/progtest/src/TestRunner.js
+++ b/progtest/src/TestRunner.js
@@ -68,7 +68,7 @@ module.exports = Class( 'TestRunner',
      *
      * @param {Array<TestCase>} dfns array of TestCases
      *
-     * @return {Array<Object<desc,i,total,failures>>} results
+     * @return {Promise} promise to complete test cases, yielding results
      */
     'public runTests'( dfns )
     {
@@ -76,13 +76,49 @@ module.exports = Class( 'TestRunner',
 
         this._reporter.preRun( total );
 
-        const results = dfns.map(
-            ( test, i ) => this._runTest( test, i, total )
+        return this._runAsync( dfns ).then(
+            results => this._reporter.done( results )
         );
+    },
 
-        this._reporter.done( results );
 
-        return results;
+    /**
+     * Run all tests asynchronously
+     *
+     * TODO: This significantly slows down the runner!  The better option
+     * would be to go back to sync and put it in a Web Worker in the client,
+     * which would also async updating of the UI.
+     *
+     * @param {Array<TestCase>} dfns test case definitions
+     *
+     * @return {Promise} promise to complete test cases, yielding results
+     */
+    'private _runAsync'( dfns )
+    {
+        const total = dfns.length;
+
+        return new Promise( resolve =>
+        {
+            const results = [];
+
+            const runNext = () =>
+            {
+                if ( dfns.length === 0 )
+                {
+                    resolve( results );
+                    return;
+                }
+
+                const dfn    = dfns.shift();
+                const result = this._runTest( dfn, results.length, total );
+
+                results.push( result );
+
+                setTimeout( runNext, 0 );
+            };
+
+            runNext();
+        } );
     },
 
 
diff --git a/progtest/test/TestRunnerTest.js b/progtest/test/TestRunnerTest.js
index fc06e04b..eff50eb9 100644
--- a/progtest/test/TestRunnerTest.js
+++ b/progtest/test/TestRunnerTest.js
@@ -86,20 +86,24 @@ describe( "TestRunner", () =>
             ]
         ];
 
-        const results = Sut( NullTestReporter(), program )
-            .runTests( test_cases );
+        Sut( NullTestReporter(), program )
+            .runTests( test_cases )
+            .then( results =>
+            {
+                test_cases.forEach( ( test_case, i ) =>
+                {
+                    const result = results[ i ];
 
-        test_cases.forEach( ( test_case, i ) =>
-        {
-            const result = results[ i ];
-
-            expect( result.desc ).to.equal( test_case.description );
-            expect( result.i ).to.equal( i );
-            expect( result.total ).to.equal(
-                Object.keys( test_case.expect ).length
-            );
-            expect( result.failures ).to.deep.equal( expect_failures[ i ] );
-        } );
+                    expect( result.desc ).to.equal( test_case.description );
+                    expect( result.i ).to.equal( i );
+                    expect( result.total ).to.equal(
+                        Object.keys( test_case.expect ).length
+                    );
+                    expect( result.failures ).to.deep.equal(
+                        expect_failures[ i ]
+                    );
+                } );
+            } );
     } );