--- a/hgsubversion/help/subversion.rst
+++ b/hgsubversion/help/subversion.rst
@@ -178,3 +178,11 @@ Please note that some of these options m
 as well, and when done so, will override the configuration. If an authormap,
 filemap or branchmap is specified, its contents will be read and stored for use
 in future pulls.
+
+Finally, the following environment variables can be used for testing a
+deployment of hgsubversion:
+
+  HGSUBVERSION_BINDINGS
+    By default, hgsubversion will use Subvertpy, but fall back to the SWIG
+    bindings. Set this variable to either ``SWIG`` or ``Subvertpy`` (case-
+    insensitive) to force that set of bindings.

--- a/hgsubversion/svnwrap/__init__.py
+++ b/hgsubversion/svnwrap/__init__.py
@@ -8,11 +8,26 @@ present.
 
 from common import *
 
-try:
+import os
+
+choice = os.environ.get('HGSUBVERSION_BINDINGS', '').lower()
+
+if choice == 'subvertpy':
     from subvertpy_wrapper import *
-except ImportError, e:
+elif choice == 'swig':
+    from svn_swig_wrapper import *
+elif choice == 'none':
+    # useful for verifying that demandimport works properly
+    raise ImportError('cannot use hgsubversion; '
+                      'bindings disabled using HGSUBVERSION_BINDINGS')
+else:
     try:
-        from svn_swig_wrapper import *
-    except ImportError:
-        # propagate the subvertpy error; it's easier to install
-        import subvertpy_wrapper
+        from subvertpy_wrapper import *
+    except ImportError, e:
+        try:
+            from svn_swig_wrapper import *
+        except ImportError:
+            # propagate the subvertpy error; it's easier to install
+            raise e
+
+del os, choice