diff --git a/vvp/vthread.cc b/vvp/vthread.cc
index 87c4637c3..a93eb4dbf 100644
--- a/vvp/vthread.cc
+++ b/vvp/vthread.cc
@@ -4321,9 +4321,9 @@ bool of_SHIFTR_I0(vthread_t thr, vvp_code_t cp)
 
 bool of_SHIFTR_S_I0(vthread_t thr, vvp_code_t cp)
 {
-      unsigned base = cp->bit_idx[0];
-      unsigned wid = cp->number;
-      unsigned long shift = thr->words[0].w_int;
+      int base = cp->bit_idx[0];
+      int wid = cp->number;
+      int shift = thr->words[0].w_int;
       vvp_bit4_t sign = thr_get_bit(thr, base+wid-1);
 
       if (thr_get_bit(thr, 4) == BIT4_1) {
@@ -4331,17 +4331,32 @@ bool of_SHIFTR_S_I0(vthread_t thr, vvp_code_t cp)
 	    vvp_vector4_t tmp (wid, BIT4_X);
 	    thr->bits4.set_vec(base, tmp);
       } else if (shift >= wid) {
-	    for (unsigned idx = 0 ;  idx < wid ;  idx += 1)
+	    for (int idx = 0 ;  idx < wid ;  idx += 1)
 		  thr_put_bit(thr, base+idx, sign);
 
       } else if (shift > 0) {
-	    for (unsigned idx = 0 ;  idx < (wid-shift) ;  idx += 1) {
+	    for (int idx = 0 ;  idx < (wid-shift) ;  idx += 1) {
 		  unsigned src = base + idx + shift;
 		  unsigned dst = base + idx;
 		  thr_put_bit(thr, dst, thr_get_bit(thr, src));
 	    }
-	    for (unsigned idx = (wid-shift) ;  idx < wid ;  idx += 1)
+	    for (int idx = (wid-shift) ;  idx < wid ;  idx += 1)
 		  thr_put_bit(thr, base+idx, sign);
+
+      } else if (shift < -wid) {
+	      // Negative shift is so far that all the value is
+	      // shifted out. Write in a constant 'bx result.
+	    vvp_vector4_t tmp (wid, BIT4_X);
+	    thr->bits4.set_vec(base, tmp);
+
+      } else if (shift < 0) {
+
+	      // For a negative shift we pad with 'bx.
+	    vvp_vector4_t tmp (thr->bits4, base, wid+shift);
+	    thr->bits4.set_vec(base-shift, tmp);
+
+	    vvp_vector4_t fil (-shift, BIT4_X);
+	    thr->bits4.set_vec(base, fil);
       }
       return true;
 }