diff --git a/mercurial/templater.py b/mercurial/templater.py
--- a/mercurial/templater.py
+++ b/mercurial/templater.py
@@ -1011,8 +1011,11 @@ class templater(object):
     def __call__(self, t, **mapping):
         ttype = t in self.map and self.map[t][0] or 'default'
         if ttype not in self.ecache:
-            self.ecache[ttype] = engines[ttype](self.load,
-                                                 self.filters, self.defaults)
+            try:
+                ecls = engines[ttype]
+            except KeyError:
+                raise error.Abort(_('invalid template engine: %s') % ttype)
+            self.ecache[ttype] = ecls(self.load, self.filters, self.defaults)
         proc = self.ecache[ttype]
 
         stream = proc.process(t, mapping)
diff --git a/tests/test-template-engine.t b/tests/test-template-engine.t
--- a/tests/test-template-engine.t
+++ b/tests/test-template-engine.t
@@ -44,4 +44,11 @@
   0 97e5f848f0936960273bbf75be6388cd0350a32b -1 0000000000000000000000000000000000000000
   -1 0000000000000000000000000000000000000000 -1 0000000000000000000000000000000000000000
 
+invalid engine type:
+
+  $ echo 'changeset = unknown:changeset.txt' > unknownenginemap
+  $ hg log --style=./unknownenginemap
+  abort: invalid template engine: unknown
+  [255]
+
   $ cd ..