diff --git a/pymodbus/client/async/__init__.py b/pymodbus/client/async/__init__.py
index d14d0dd32..683984697 100644
--- a/pymodbus/client/async/__init__.py
+++ b/pymodbus/client/async/__init__.py
@@ -31,4 +31,14 @@
     # For asyncio the actual client is returned and event loop is asyncio loop
 
 """
-from pymodbus.client.async.deprecated.async import *
+from pymodbus.compat import is_installed
+
+installed = is_installed('twisted')
+if installed:
+    # Import deprecated async client only if twisted is installed #338
+    from pymodbus.client.async.deprecated.async import *
+else:
+    import logging
+    logger = logging.getLogger(__name__)
+    logger.warning("Not Importing deprecated clients. "
+                   "Dependency Twisted is not Installed")
diff --git a/pymodbus/client/async/deprecated/__init__.py b/pymodbus/client/async/deprecated/__init__.py
index 902761faf..02d241a44 100644
--- a/pymodbus/client/async/deprecated/__init__.py
+++ b/pymodbus/client/async/deprecated/__init__.py
@@ -43,5 +43,5 @@
 """
 
 
-def deprecated(name): # pragma: no cover
+def deprecated(name):  # pragma: no cover
     warnings.warn(WARNING.format(name), DeprecationWarning)
diff --git a/pymodbus/compat.py b/pymodbus/compat.py
index cdb0a31fe..48920ba74 100644
--- a/pymodbus/compat.py
+++ b/pymodbus/compat.py
@@ -58,6 +58,16 @@
     implements_to_string = lambda x: x
 
     byte2int = lambda b: b
+    if PYTHON_VERSION >= (3, 4):
+        def is_installed(module):
+            import importlib.util
+            found = importlib.util.find_spec(module)
+            return found
+    else:
+        def is_installed(module):
+            import importlib
+            found = importlib.find_loader(module)
+            return found
 # --------------------------------------------------------------------------- #
 # python > 2.5 compatability layer
 # --------------------------------------------------------------------------- #
@@ -76,3 +86,11 @@ def implements_to_string(klass):
         klass.__unicode__ = klass.__str__
         klass.__str__ = lambda x: x.__unicode__().encode('utf-8')
         return klass
+
+    def is_installed(module):
+        import imp
+        try:
+            imp.find_module(module)
+            return True
+        except ImportError:
+            return False
\ No newline at end of file