diff --git a/vvp/vpi_signal.cc b/vvp/vpi_signal.cc
index dfe454d9c..d5a4203e1 100644
--- a/vvp/vpi_signal.cc
+++ b/vvp/vpi_signal.cc
@@ -989,6 +989,15 @@ static int PV_get_base(struct __vpiPV*rfp)
 	/* We return from the symbol base if it is defined. */
       if (rfp->sbase != 0) {
 	    s_vpi_value val;
+	      /* Check to see if the value is defined. */
+	    val.format = vpiVectorVal;
+	    vpi_get_value(rfp->sbase, &val);
+	    int words = (vpi_get(vpiSize, rfp->sbase)-1)/32 + 1;
+	    for(int idx = 0; idx < words; idx += 1) {
+		    /* Return INT_MIN to indicate an X base. */
+		  if (val.value.vector[idx].bval != 0) return INT_MIN;
+	    }
+	      /* The value is defined so get and return it. */
 	    val.format = vpiIntVal;
 	    vpi_get_value(rfp->sbase, &val);
 	    return val.value.integer;