diff --git a/gns3server/modules/dynamips/nodes/router.py b/gns3server/modules/dynamips/nodes/router.py
index 45f0feea..39165f1c 100644
--- a/gns3server/modules/dynamips/nodes/router.py
+++ b/gns3server/modules/dynamips/nodes/router.py
@@ -271,6 +271,20 @@ class Router(object):
             self.resume()
         else:
 
+            if not os.path.isfile(self._image):
+                raise DynamipsError("IOS image '{}' is not accessible".format(self._image))
+
+            try:
+                with open(self._image, "rb") as f:
+                    # read the first 7 bytes of the file.
+                    elf_header_start = f.read(7)
+            except OSError as e:
+                raise DynamipsError("Cannot read ELF header for IOS image {}: {}".format(self._image, e))
+
+            # IOS images must start with the ELF magic number, be 32-bit, big endian and have an ELF version of 1
+            if elf_header_start != b'\x7fELF\x01\x02\x01':
+                raise DynamipsError("'{}' is not a valid IOU image".format(self._image))
+
             if self.console and self.aux:
                 # check that console and aux ports are available
                 try:
diff --git a/gns3server/modules/iou/iou_device.py b/gns3server/modules/iou/iou_device.py
index f56d38b3..517be45d 100644
--- a/gns3server/modules/iou/iou_device.py
+++ b/gns3server/modules/iou/iou_device.py
@@ -414,8 +414,23 @@ class IOUDevice(object):
 
         if not self.is_running():
 
-            if not os.path.isfile(self._path):
-                raise IOUError("IOU '{}' is not accessible".format(self._path))
+            if not os.path.isfile(iou_path):
+                raise IOUError("IOU image '{}' is not accessible".format(iou_path))
+
+            try:
+                with open(iou_path, "rb") as f:
+                    # read the first 7 bytes of the file.
+                    elf_header_start = f.read(7)
+            except OSError as e:
+                raise IOUError("Cannot read ELF header for IOU image '{}': {}".format(self._path, e))
+
+            # IOU images must start with the ELF magic number, be 32-bit, little endian
+            # and have an ELF version of 1 normal IOS image are big endian!
+            if elf_header_start != b'\x7fELF\x01\x01\x01':
+                raise IOUError("'{}' is not a valid IOU image".format(self._path))
+
+            if not os.access(self._path, os.X_OK):
+                raise IOUError("IOU image '{}' is not executable".format(self._path))
 
             if not self._iourc or not os.path.isfile(self._iourc):
                 raise IOUError("A iourc file is necessary to start IOU")