diff --git a/openmc/executor.py b/openmc/executor.py
index 75094e7388f..44ed1b80b1f 100644
--- a/openmc/executor.py
+++ b/openmc/executor.py
@@ -92,6 +92,36 @@ def _process_CLI_arguments(volume=False, geometry_debug=False, particles=None,
     return args
 
 
+def _get_error_message(output):
+    """Get the error message from the output of a failed OpenMC run
+
+    Parameters
+    ----------
+    output : str
+        Standard output and standard error of the OpenMC executable
+
+    Returns
+    -------
+    str
+        Error message with whitespace simplified
+
+    """
+    if 'ERROR: ' in output:
+        _, _, error_msg = output.partition('ERROR: ')
+    elif 'what()' in output:
+        _, _, error_msg = output.partition('what(): ')
+    elif 'terminating due to uncaught exception of type ' in output:
+        # libc++ (e.g. macOS) reports "...of type std::runtime_error: msg"
+        _, _, error_msg = output.partition(
+            'terminating due to uncaught exception of type ')
+        _, sep, error_msg = error_msg.partition(': ')
+        if not sep or not error_msg.strip():
+            error_msg = 'OpenMC aborted unexpectedly.'
+    else:
+        error_msg = 'OpenMC aborted unexpectedly.'
+    return ' '.join(error_msg.split())
+
+
 def _run(args, output, cwd):
     # Launch a subprocess
     p = subprocess.Popen(args, cwd=cwd, stdout=subprocess.PIPE,
@@ -113,17 +143,7 @@ def _run(args, output, cwd):
 
     # Raise an exception if return status is non-zero
     if p.returncode != 0:
-        # Get error message from output and simplify whitespace
-        output = ''.join(lines)
-        if 'ERROR: ' in output:
-            _, _, error_msg = output.partition('ERROR: ')
-        elif 'what()' in output:
-            _, _, error_msg = output.partition('what(): ')
-        else:
-            error_msg = 'OpenMC aborted unexpectedly.'
-        error_msg = ' '.join(error_msg.split())
-
-        raise RuntimeError(error_msg)
+        raise RuntimeError(_get_error_message(''.join(lines)))
 
 
 def plot_geometry(output=True, openmc_exec='openmc', cwd='.', path_input=None):
diff --git a/tests/unit_tests/test_executor.py b/tests/unit_tests/test_executor.py
new file mode 100644
index 00000000000..0460b10c27f
--- /dev/null
+++ b/tests/unit_tests/test_executor.py
@@ -0,0 +1,43 @@
+import io
+import subprocess
+
+import openmc
+from openmc.executor import _get_error_message
+import pytest
+
+
+@pytest.mark.parametrize('output, message', [
+    # OpenMC's own error messages
+    (' ERROR: Could not add nuclide', 'Could not add nuclide'),
+    # libstdc++ (e.g. Linux)
+    ("terminate called after throwing an instance of 'std::runtime_error'\n"
+     "  what():  Could not add nuclide", 'Could not add nuclide'),
+    # libc++ (e.g. macOS)
+    ('libc++abi: terminating due to uncaught exception of type '
+     'std::runtime_error: Could not add nuclide', 'Could not add nuclide'),
+    # libc++ with an exception that has no message
+    ('libc++abi: terminating due to uncaught exception of type int',
+     'OpenMC aborted unexpectedly.'),
+    # Any other failure
+    ('Segmentation fault', 'OpenMC aborted unexpectedly.'),
+])
+def test_error_message_from_output(output, message):
+    """The error message is recovered from each way OpenMC can fail."""
+    assert _get_error_message(output) == message
+
+
+def test_failed_run_raises_error_message(monkeypatch):
+    """A failed run raises a RuntimeError with the message from its output."""
+    class FailedProcess:
+        def __init__(self, *args, **kwargs):
+            self.stdout = io.StringIO(
+                'libc++abi: terminating due to uncaught exception of type '
+                'std::runtime_error: Could not add nuclide\n')
+            self.returncode = 1
+
+        def poll(self):
+            return self.returncode
+
+    monkeypatch.setattr(subprocess, 'Popen', FailedProcess)
+    with pytest.raises(RuntimeError, match='^Could not add nuclide$'):
+        openmc.plot_geometry(output=False)