diff --git a/src_Core/RISCY_OOO/procs/RV64G_OOO/FetchStage.bsv b/src_Core/RISCY_OOO/procs/RV64G_OOO/FetchStage.bsv
index 4a6c132..2c4d498 100644
--- a/src_Core/RISCY_OOO/procs/RV64G_OOO/FetchStage.bsv
+++ b/src_Core/RISCY_OOO/procs/RV64G_OOO/FetchStage.bsv
@@ -746,7 +746,7 @@ module mkFetchStage(FetchStage);
                         end
                      end else if (!isValid(nextPc)) begin
                         // A Jr will jump; if we don't have a record, we should wait to prevent wasted work.
-                        nextPc = Valid (0); // Dummy value to prevent progress.
+                        nextPc = Valid ({2'b01,?}); // Invalid virtual address to prevent progress.
                      end
                   end
 
diff --git a/src_Core/RISCY_OOO/procs/lib/ITlb.bsv b/src_Core/RISCY_OOO/procs/lib/ITlb.bsv
index 17fb4a4..3761abc 100644
--- a/src_Core/RISCY_OOO/procs/lib/ITlb.bsv
+++ b/src_Core/RISCY_OOO/procs/lib/ITlb.bsv
@@ -304,7 +304,8 @@ module mkITlb(ITlb::ITlb);
                 else if (vm_info.sv39) begin
                     let vpn = getVpn(vaddr);
                     let trans_result = tlb.translate(vpn, vm_info.asid);
-                    if (trans_result.hit) begin
+                    if (!validVirtualAddress(vaddr)) hitQ.enq(tuple3(?, Valid (excInstPageFault), False));
+                    else if (trans_result.hit) begin
                         // TLB hit
                         let entry = trans_result.entry;
                         // check permission
diff --git a/src_Core/RISCY_OOO/procs/lib/TlbTypes.bsv b/src_Core/RISCY_OOO/procs/lib/TlbTypes.bsv
index 8c8330b..f189852 100644
--- a/src_Core/RISCY_OOO/procs/lib/TlbTypes.bsv
+++ b/src_Core/RISCY_OOO/procs/lib/TlbTypes.bsv
@@ -1,6 +1,6 @@
 
 // Copyright (c) 2017 Massachusetts Institute of Technology
-// 
+//
 // Permission is hereby granted, free of charge, to any person
 // obtaining a copy of this software and associated documentation
 // files (the "Software"), to deal in the Software without
@@ -8,10 +8,10 @@
 // modify, merge, publish, distribute, sublicense, and/or sell copies
 // of the Software, and to permit persons to whom the Software is
 // furnished to do so, subject to the following conditions:
-// 
+//
 // The above copyright notice and this permission notice shall be
 // included in all copies or substantial portions of the Software.
-// 
+//
 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
@@ -51,7 +51,7 @@ typedef 44 PpnSz;
 typedef Bit#(PpnSz) Ppn;
 typedef 12 PageOffsetSz; // 4KB basic page
 typedef Bit#(PageOffsetSz) PageOffset;
-typedef 9 VpnIdxSz; // Vpn is broken down to 3 indexes to 3 levels of page table 
+typedef 9 VpnIdxSz; // Vpn is broken down to 3 indexes to 3 levels of page table
 typedef Bit#(VpnIdxSz) VpnIdx;
 typedef Bit#(2) PageWalkLevel; // 2: 1GB page, 1: 2MB page, 0: 4KB page
 typedef 3 NumPageWalkLevels;
@@ -99,6 +99,9 @@ function Vpn getVpn(Addr addr) = addr[38:12];
 
 function PageOffset getPageOffset(Addr addr) = truncate(addr);
 
+// All the upper bits should be equal for a valid SV39 virtual address.
+function Bool validVirtualAddress(Addr addr) = ((^addr[63:39]) == 0);
+
 function Addr getPTBaseAddr(Ppn basePpn);
     PageOffset offset = 0;
     return zeroExtend({basePpn, offset});