diff --git a/src/devices/csma/csma-net-device.cc b/src/devices/csma/csma-net-device.cc
index a1e42361c..d2ed00edb 100644
--- a/src/devices/csma/csma-net-device.cc
+++ b/src/devices/csma/csma-net-device.cc
@@ -393,6 +393,20 @@ CsmaNetDevice::AddHeader (Ptr<Packet> p,   Mac48Address source,  Mac48Address de
       // in the old Ethernet Blue Book.
       //
       lengthType = protocolNumber;
+
+      //
+      // All Ethernet frames must carry a minimum payload of 46 bytes.  We need
+      // to pad out if we don't have enough bytes.  These must be real bytes 
+      // since they will be written to pcap files and compared in regression 
+      // trace files.
+      //
+      if (p->GetSize () < 46)
+        {
+          uint8_t buffer[46];
+          memset (buffer, 0, 46);
+          Ptr<Packet> padd = Create<Packet> (buffer, 46 - p->GetSize ());
+          p->AddAtEnd (padd);
+        }
       break;
     case LLC: 
       {
@@ -401,6 +415,21 @@ CsmaNetDevice::AddHeader (Ptr<Packet> p,   Mac48Address source,  Mac48Address de
         LlcSnapHeader llc;
         llc.SetType (protocolNumber);
         p->AddHeader (llc);
+
+        //
+        // All Ethernet frames must carry a minimum payload of 46 bytes.  The 
+        // LLC SNAP header counts as part of this payload.  We need to padd out
+        // if we don't have enough bytes.  These must be real bytes since they 
+        // will be written to pcap files and compared in regression trace files.
+        //
+        if (p->GetSize () < 46)
+          {
+            uint8_t buffer[46];
+            memset (buffer, 0, 46);
+            Ptr<Packet> padd = Create<Packet> (buffer, 46 - p->GetSize ());
+            p->AddAtEnd (padd);
+          }
+
         //
         // This corresponds to the length interpretation of the lengthType field,
         // but with an LLC/SNAP header added to the payload as in IEEE 802.2