diff --git a/vpi/sys_convert.c b/vpi/sys_convert.c
index 4b6ce77f3..9c387aabd 100644
--- a/vpi/sys_convert.c
+++ b/vpi/sys_convert.c
@@ -215,7 +215,10 @@ static PLI_INT32 sys_rtoi_calltf(PLI_BYTE8*user)
     vpi_get_value(arg, &value);
 
     /* convert */
-    res.aval = (unsigned)value.value.real;
+    if (value.value.real >= 0.0)
+      res.aval = (unsigned)value.value.real;
+    else
+      res.aval = - (unsigned)-value.value.real;
     res.bval = 0;
 
     value.format = vpiVectorVal;
diff --git a/vpi/sys_random.c b/vpi/sys_random.c
index b152a4ed8..d0a3cb251 100644
--- a/vpi/sys_random.c
+++ b/vpi/sys_random.c
@@ -187,7 +187,7 @@ long rtl_dist_uniform(long *seed, long start, long end)
             if (r >= 0) {
                   i = (unsigned long) r;
             } else {
-                  i = (unsigned long) (r - 1);
+	          i = - ( (unsigned long) (-(r - 1)) );
             }
             if (i < start) i = start;
             if (i >= end) i = end - 1;
@@ -197,7 +197,7 @@ long rtl_dist_uniform(long *seed, long start, long end)
             if (r >= 0) {
                   i = (unsigned long) r;
             } else {
-                  i = (unsigned long) (r - 1);
+	          i = - ( (unsigned long) (-(r - 1)) );
             }
             if (i <= start) i = start + 1;
             if (i > end) i = end;
@@ -208,7 +208,12 @@ long rtl_dist_uniform(long *seed, long start, long end)
             if (r >= 0) {
                   i = (unsigned long) r;
             } else {
-                  i = (unsigned long) (r - 1);
+	            /* At least some compilers will notice that (r-1)
+		       is <0 when castling to unsigned long and
+		       replace the result with a zero. This causes
+		       much wrongness, so do the casting to the
+		       positive version and invert it back. */
+	          i = - ( (unsigned long) (-(r - 1)) );
             }
       }