diff --git a/vvp/vthread.cc b/vvp/vthread.cc
index 6ff26126e..d15e61cd2 100644
--- a/vvp/vthread.cc
+++ b/vvp/vthread.cc
@@ -4205,9 +4205,9 @@ bool of_SET_X0(vthread_t thr, vvp_code_t cp)
 
 bool of_SHIFTL_I0(vthread_t thr, vvp_code_t cp)
 {
-      unsigned base = cp->bit_idx[0];
-      unsigned wid = cp->number;
-      long shift = thr->words[0].w_int;
+      int base = cp->bit_idx[0];
+      int wid = cp->number;
+      int shift = thr->words[0].w_int;
 
       assert(base >= 4);
       thr_check_addr(thr, base+wid-1);
@@ -4217,7 +4217,7 @@ bool of_SHIFTL_I0(vthread_t thr, vvp_code_t cp)
 	    vvp_vector4_t tmp (wid, BIT4_X);
 	    thr->bits4.set_vec(base, tmp);
 
-      } else if (shift >= (long)wid) {
+      } else if (shift >= wid) {
 	      // Shift is so far that all value is shifted out. Write
 	      // in a constant 0 result.
 	    vvp_vector4_t tmp (wid, BIT4_0);
@@ -4231,9 +4231,13 @@ bool of_SHIFTL_I0(vthread_t thr, vvp_code_t cp)
 	    vvp_vector4_t fil (shift, BIT4_0);
 	    thr->bits4.set_vec(base, fil);
 
+      } else if (shift <= -wid) {
+	    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.
-	    unsigned idx;
+	    int idx;
 	    for (idx = 0 ;  (idx-shift) < wid ;  idx += 1) {
 		  unsigned src = base + idx - shift;
 		  unsigned dst = base + idx;
@@ -4255,9 +4259,9 @@ bool of_SHIFTL_I0(vthread_t thr, vvp_code_t cp)
  */
 bool of_SHIFTR_I0(vthread_t thr, vvp_code_t cp)
 {
-      unsigned base = cp->bit_idx[0];
-      unsigned wid = cp->number;
-      long shift = thr->words[0].w_int;
+      int base = cp->bit_idx[0];
+      int wid = cp->number;
+      int shift = thr->words[0].w_int;
 
       assert(base >= 4);
       thr_check_addr(thr, base+wid-1);
@@ -4279,7 +4283,7 @@ bool of_SHIFTR_I0(vthread_t thr, vvp_code_t cp)
 	    vvp_vector4_t tmp (shift, BIT4_0);
 	    thr->bits4.set_vec(base+wid-shift, tmp);
 
-      } else if (shift < -(long)wid) {
+      } 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);