diff --git a/gns3server/modules/dynamips/dynamips_hypervisor.py b/gns3server/modules/dynamips/dynamips_hypervisor.py
index 45e6449b..1ddc4c02 100644
--- a/gns3server/modules/dynamips/dynamips_hypervisor.py
+++ b/gns3server/modules/dynamips/dynamips_hypervisor.py
@@ -351,8 +351,6 @@ class DynamipsHypervisor(object):
             socket_type = socket.SOCK_STREAM
 
         for port in range(start_port, end_port):
-            if port + 1 == end_port:
-                raise DynamipsError("Could not find a free port between {0} and {1}".format(start_port, end_port))
             try:
                 if ":" in host:
                     # IPv6 address support
@@ -364,7 +362,10 @@ class DynamipsHypervisor(object):
                 return port
             except OSError as e:
                 if e.errno == errno.EADDRINUSE:  # socket already in use
-                    continue
+                    if port + 1 == end_port:
+                        raise DynamipsError("Could not find a free port between {0} and {1}".format(start_port, end_port))
+                    else:
+                        continue
                 else:
                     raise DynamipsError("Could not find an unused port: {}".format(e))
 
diff --git a/gns3server/modules/iou/iou_device.py b/gns3server/modules/iou/iou_device.py
index 5d0940fb..6a53039d 100644
--- a/gns3server/modules/iou/iou_device.py
+++ b/gns3server/modules/iou/iou_device.py
@@ -793,8 +793,6 @@ class IOUDevice(object):
             socket_type = socket.SOCK_STREAM
 
         for port in range(start_port, end_port):
-            if port + 1 == end_port:
-                raise IOUError("Could not find a free port between {0} and {1}".format(start_port, end_port))
             try:
                 if ":" in host:
                     # IPv6 address support
@@ -806,6 +804,9 @@ class IOUDevice(object):
                 return port
             except OSError as e:
                 if e.errno == errno.EADDRINUSE:  # socket already in use
-                    continue
+                    if port + 1 == end_port:
+                        raise IOUError("Could not find a free port between {0} and {1}".format(start_port, end_port))
+                    else:
+                        continue
                 else:
                     raise IOUError("Could not find an unused port: {}".format(e))