diff --git a/gns3server/modules/iou/__init__.py b/gns3server/modules/iou/__init__.py
index 5ae65f98..e7d2c0c6 100644
--- a/gns3server/modules/iou/__init__.py
+++ b/gns3server/modules/iou/__init__.py
@@ -69,18 +69,15 @@ class IOU(IModule):
         iou_config = config.get_section_config(name.upper())
         self._iouyap = iou_config.get("iouyap")
         if not self._iouyap or not os.path.isfile(self._iouyap):
-            iouyap_in_cwd = os.path.join(os.getcwd(), "iouyap")
-            if os.path.isfile(iouyap_in_cwd):
-                self._iouyap = iouyap_in_cwd
-            else:
-                # look for iouyap if none is defined or accessible
-                for path in os.environ["PATH"].split(":"):
-                    try:
-                        if "iouyap" in os.listdir(path) and os.access(os.path.join(path, "iouyap"), os.X_OK):
-                            self._iouyap = os.path.join(path, "iouyap")
-                            break
-                    except OSError:
-                        continue
+            paths = [os.getcwd()] + os.environ["PATH"].split(":")
+            # look for iouyap in the current working directory and $PATH
+            for path in paths:
+                try:
+                    if "iouyap" in os.listdir(path) and os.access(os.path.join(path, "iouyap"), os.X_OK):
+                        self._iouyap = os.path.join(path, "iouyap")
+                        break
+                except OSError:
+                    continue
 
         if not self._iouyap:
             log.warning("iouyap binary couldn't be found!")
diff --git a/gns3server/modules/vpcs/__init__.py b/gns3server/modules/vpcs/__init__.py
index 3ef9347c..5c31310a 100644
--- a/gns3server/modules/vpcs/__init__.py
+++ b/gns3server/modules/vpcs/__init__.py
@@ -66,18 +66,15 @@ class VPCS(IModule):
         vpcs_config = config.get_section_config(name.upper())
         self._vpcs = vpcs_config.get("vpcs")
         if not self._vpcs or not os.path.isfile(self._vpcs):
-            vpcs_in_cwd = os.path.join(os.getcwd(), "vpcs")
-            if os.path.isfile(vpcs_in_cwd):
-                self._vpcs = vpcs_in_cwd
-            else:
-                # look for vpcs if none is defined or accessible
-                for path in os.environ["PATH"].split(":"):
-                    try:
-                        if "vpcs" in os.listdir(path) and os.access(os.path.join(path, "vpcs"), os.X_OK):
-                            self._vpcs = os.path.join(path, "vpcs")
-                            break
-                    except OSError:
-                        continue
+            paths = [os.getcwd()] + os.environ["PATH"].split(":")
+            # look for VPCS in the current working directory and $PATH
+            for path in paths:
+                try:
+                    if "vpcs" in os.listdir(path) and os.access(os.path.join(path, "vpcs"), os.X_OK):
+                        self._vpcs = os.path.join(path, "vpcs")
+                        break
+                except OSError:
+                    continue
 
         if not self._vpcs:
             log.warning("VPCS binary couldn't be found!")
@@ -241,6 +238,9 @@ class VPCS(IModule):
             except OSError as e:
                 raise VPCSError("Could not create working directory {}".format(e))
 
+            if not self._vpcs:
+                raise VPCSError("No path to a VPCS executable has been set")
+
             vpcs_instance = VPCSDevice(self._vpcs,
                                        self._working_dir,
                                        self._host,
diff --git a/gns3server/modules/vpcs/vpcs_device.py b/gns3server/modules/vpcs/vpcs_device.py
index 5e3263bb..23bd6970 100644
--- a/gns3server/modules/vpcs/vpcs_device.py
+++ b/gns3server/modules/vpcs/vpcs_device.py
@@ -321,6 +321,9 @@ class VPCSDevice(object):
 
         if not self.is_running():
 
+            if not self._path:
+                raise VPCSError("No path to a VPCS executable has been set")
+
             if not os.path.isfile(self._path):
                 raise VPCSError("VPCS '{}' is not accessible".format(self._path))