diff --git a/bots/naughty/debian-stable/9641-xtermjs-dimensions-crash b/bots/naughty/debian-stable/9641-xtermjs-dimensions-crash
index 086fd234110b..92d68521e068 100644
--- a/bots/naughty/debian-stable/9641-xtermjs-dimensions-crash
+++ b/bots/naughty/debian-stable/9641-xtermjs-dimensions-crash
@@ -1,5 +1,4 @@
 Traceback (most recent call last):
   File "test/verify/check-machines", line *, in testSerialConsole
-    b.wait_not_present("div.terminal canvas.xterm-text-layer")
 *
-Error: timeout
+RuntimeError: TypeError: Cannot read property 'dimensions' of undefined
diff --git a/bots/naughty/debian-testing/9641-xtermjs-dimensions-crash b/bots/naughty/debian-testing/9641-xtermjs-dimensions-crash
index 086fd234110b..92d68521e068 100644
--- a/bots/naughty/debian-testing/9641-xtermjs-dimensions-crash
+++ b/bots/naughty/debian-testing/9641-xtermjs-dimensions-crash
@@ -1,5 +1,4 @@
 Traceback (most recent call last):
   File "test/verify/check-machines", line *, in testSerialConsole
-    b.wait_not_present("div.terminal canvas.xterm-text-layer")
 *
-Error: timeout
+RuntimeError: TypeError: Cannot read property 'dimensions' of undefined
diff --git a/bots/naughty/fedora-27/9641-xtermjs-dimensions-crash b/bots/naughty/fedora-27/9641-xtermjs-dimensions-crash
index 086fd234110b..92d68521e068 100644
--- a/bots/naughty/fedora-27/9641-xtermjs-dimensions-crash
+++ b/bots/naughty/fedora-27/9641-xtermjs-dimensions-crash
@@ -1,5 +1,4 @@
 Traceback (most recent call last):
   File "test/verify/check-machines", line *, in testSerialConsole
-    b.wait_not_present("div.terminal canvas.xterm-text-layer")
 *
-Error: timeout
+RuntimeError: TypeError: Cannot read property 'dimensions' of undefined
diff --git a/bots/naughty/fedora-28/9641-xtermjs-dimensions-crash b/bots/naughty/fedora-28/9641-xtermjs-dimensions-crash
index 086fd234110b..92d68521e068 100644
--- a/bots/naughty/fedora-28/9641-xtermjs-dimensions-crash
+++ b/bots/naughty/fedora-28/9641-xtermjs-dimensions-crash
@@ -1,5 +1,4 @@
 Traceback (most recent call last):
   File "test/verify/check-machines", line *, in testSerialConsole
-    b.wait_not_present("div.terminal canvas.xterm-text-layer")
 *
-Error: timeout
+RuntimeError: TypeError: Cannot read property 'dimensions' of undefined
diff --git a/bots/naughty/rhel-7/9641-xtermjs-dimensions-crash b/bots/naughty/rhel-7/9641-xtermjs-dimensions-crash
index 086fd234110b..92d68521e068 100644
--- a/bots/naughty/rhel-7/9641-xtermjs-dimensions-crash
+++ b/bots/naughty/rhel-7/9641-xtermjs-dimensions-crash
@@ -1,5 +1,4 @@
 Traceback (most recent call last):
   File "test/verify/check-machines", line *, in testSerialConsole
-    b.wait_not_present("div.terminal canvas.xterm-text-layer")
 *
-Error: timeout
+RuntimeError: TypeError: Cannot read property 'dimensions' of undefined
diff --git a/bots/naughty/rhel-x/9641-xtermjs-dimensions-crash b/bots/naughty/rhel-x/9641-xtermjs-dimensions-crash
index 086fd234110b..92d68521e068 100644
--- a/bots/naughty/rhel-x/9641-xtermjs-dimensions-crash
+++ b/bots/naughty/rhel-x/9641-xtermjs-dimensions-crash
@@ -1,5 +1,4 @@
 Traceback (most recent call last):
   File "test/verify/check-machines", line *, in testSerialConsole
-    b.wait_not_present("div.terminal canvas.xterm-text-layer")
 *
-Error: timeout
+RuntimeError: TypeError: Cannot read property 'dimensions' of undefined
diff --git a/bots/naughty/ubuntu-1604/9641-xtermjs-dimensions-crash b/bots/naughty/ubuntu-1604/9641-xtermjs-dimensions-crash
index 086fd234110b..92d68521e068 100644
--- a/bots/naughty/ubuntu-1604/9641-xtermjs-dimensions-crash
+++ b/bots/naughty/ubuntu-1604/9641-xtermjs-dimensions-crash
@@ -1,5 +1,4 @@
 Traceback (most recent call last):
   File "test/verify/check-machines", line *, in testSerialConsole
-    b.wait_not_present("div.terminal canvas.xterm-text-layer")
 *
-Error: timeout
+RuntimeError: TypeError: Cannot read property 'dimensions' of undefined
diff --git a/bots/naughty/ubuntu-stable/9641-xtermjs-dimensions-crash b/bots/naughty/ubuntu-stable/9641-xtermjs-dimensions-crash
index 086fd234110b..92d68521e068 100644
--- a/bots/naughty/ubuntu-stable/9641-xtermjs-dimensions-crash
+++ b/bots/naughty/ubuntu-stable/9641-xtermjs-dimensions-crash
@@ -1,5 +1,4 @@
 Traceback (most recent call last):
   File "test/verify/check-machines", line *, in testSerialConsole
-    b.wait_not_present("div.terminal canvas.xterm-text-layer")
 *
-Error: timeout
+RuntimeError: TypeError: Cannot read property 'dimensions' of undefined
diff --git a/test/common/cdp-driver.js b/test/common/cdp-driver.js
index 72dfbd81d5ae..018fbe3ec73f 100755
--- a/test/common/cdp-driver.js
+++ b/test/common/cdp-driver.js
@@ -47,11 +47,15 @@ function fatal() {
 }
 
 function fail(err) {
+    if (typeof err === 'undefined')
+        err = null;
     process.stdout.write(JSON.stringify({"error": err}) + '\n');
 }
 
 function success(result) {
-    process.stdout.write(JSON.stringify({"result": result === undefined ? null : result}) + '\n');
+    if (typeof result === 'undefined')
+        result = null;
+    process.stdout.write(JSON.stringify({"result": result}) + '\n');
 }
 
 /**
@@ -61,6 +65,7 @@ function success(result) {
 var messages = [];
 var logPromiseResolver;
 var nReportedLogMessages = 0;
+var unhandledExceptions = [];
 
 function setupLogging(client) {
     client.Runtime.enable();
@@ -72,6 +77,16 @@ function setupLogging(client) {
         resolveLogPromise();
     });
 
+    client.Runtime.exceptionThrown(info => {
+        let details = info.exceptionDetails;
+        // don't log test timeouts, they already get handled
+        if (details.exception && details.exception.className === "PhWaitCondTimeout")
+            return;
+
+        unhandledExceptions.push(details)
+        process.stderr.write(details.description || JSON.stringify(details) + "\n");
+    });
+
     client.Log.enable();
     client.Log.entryAdded(entry => {
         let msg = entry["entry"];
@@ -288,7 +303,19 @@ CDP.New(options)
                                 pageLoadPromise = new Promise((resolve, reject) => { pageLoadResolve = resolve; pageLoadReject = reject; });
 
                             // run the command
-                            eval(command).then(success, fail);
+                            eval(command).then(reply => {
+                                if (unhandledExceptions.length === 0) {
+                                    success(reply);
+                                } else {
+                                    let details = unhandledExceptions[0];
+                                    let message = details.exception.message ||
+                                                  details.exception.description ||
+                                                  details.exception.value ||
+                                                  JSON.stringify(details.exception);
+                                    fail(message.split("\n")[0]);
+                                    unhandledExceptions.length = 0;
+                                }
+                            }, fail);
 
                             input_buf = input_buf.slice(i+1);
                         }
diff --git a/test/common/test-functions.js b/test/common/test-functions.js
index 93d1caf4a4f1..0d5816cd9d67 100644
--- a/test/common/test-functions.js
+++ b/test/common/test-functions.js
@@ -184,6 +184,12 @@ function ph_focus(sel)
     ph_find(sel).focus();
 }
 
+class PhWaitCondTimeout extends Error {
+    constructor() {
+        super("condition did not become true");
+    }
+}
+
 function ph_wait_cond(cond, timeout) {
     return new Promise((resolve, reject) => {
         // poll every 100 ms for now;  FIXME: poll less often and re-check on mutations using
@@ -192,7 +198,7 @@ function ph_wait_cond(cond, timeout) {
         let tm = window.setTimeout( () => {
                 if (stepTimer)
                     window.clearTimeout(stepTimer);
-                reject("condition did not become true");
+                reject(new PhWaitCondTimeout());
             }, timeout);
         function step() {
             try {