diff --git a/gmsh_interop/runner.py b/gmsh_interop/runner.py
index d0082235ab9522dc420f65fdd23e0e768d156ff0..1fdc6cdaf6db871a472583d22530b41a4a1a3ac5 100644
--- a/gmsh_interop/runner.py
+++ b/gmsh_interop/runner.py
@@ -1,3 +1,32 @@
+from __future__ import division, absolute_import
+
+__copyright__ = """
+Copyright (C) 2017 Andreas Kloeckner
+Copyright (C) 2018 Alexandru Fikl
+"""
+
+__license__ = """
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+"""
+
+from pytools import memoize_method
+
 import logging
 logger = logging.getLogger(__name__)
 
@@ -95,7 +124,8 @@ class GmshRunner(object):
     def __init__(self, source, dimensions=None, order=None,
             incomplete_elements=None, other_options=[],
             extension="geo", gmsh_executable="gmsh",
-            output_file_name="output.msh"):
+            output_file_name="output.msh",
+            target_unit=None):
         if isinstance(source, str):
             from warnings import warn
             warn("passing a string as 'source' is deprecated--use "
@@ -104,6 +134,12 @@ class GmshRunner(object):
 
             source = ScriptSource(source, extension)
 
+        if target_unit is None:
+            target_unit = "MM"
+            from warnings import warn
+            warn("Not specifying target_unit is deprecated. Set target_unit='MM' "
+                "to retain prior behavior.", DeprecationWarning, stacklevel=2)
+
         self.source = source
         self.dimensions = dimensions
         self.order = order
@@ -111,10 +147,29 @@ class GmshRunner(object):
         self.other_options = other_options
         self.gmsh_executable = gmsh_executable
         self.output_file_name = output_file_name
+        self.target_unit = target_unit.upper()
 
-        if dimensions not in [1, 2, 3, None]:
+        if self.dimensions not in [1, 2, 3, None]:
             raise RuntimeError("dimensions must be one of 1,2,3 or None")
 
+        if self.target_unit not in ['M', 'MM']:
+            raise RuntimeError("units must be 'M' (meters) or 'MM' (millimeters)")
+
+    @property
+    @memoize_method
+    def version(self):
+        from distutils.version import LooseVersion
+        cmdline = [
+                self.gmsh_executable,
+                '-version'
+                ]
+
+        from pytools.prefork import call_capture_output
+        retcode, stdout, stderr = call_capture_output(cmdline)
+
+        version = stderr.decode().strip()
+        return LooseVersion(version)
+
     def __enter__(self):
         self.temp_dir_mgr = None
         temp_dir_mgr = _TempDirManager()
@@ -154,6 +209,15 @@ class GmshRunner(object):
                     "-nopopup",
                     "-format", "msh2"]
 
+            # NOTE: handle unit incompatibility introduced in GMSH4
+            # https://gitlab.onelab.info/gmsh/gmsh/issues/397
+            if self.version < '4.0.0':
+                if self.target_unit == 'M':
+                    cmdline.extend(["-string", "Geometry.OCCScaling=1000;"])
+            else:
+                cmdline.extend(["-string",
+                    "Geometry.OCCTargetUnit='{}';".format(self.target_unit)])
+
             if self.dimensions is not None:
                 cmdline.append("-%d" % self.dimensions)