diff --git a/Basic/Core/Core.xs b/Basic/Core/Core.xs
index c19c399eb..6a00fc7db 100644
--- a/Basic/Core/Core.xs
+++ b/Basic/Core/Core.xs
@@ -140,6 +140,7 @@ void
 firstvals_nophys(x)
   pdl *x
   PPCODE:
+    if (!(x->state & PDL_ALLOCATED)) barf("firstvals_nophys called on non-ALLOCATED", x);
     PDL_Indx i, maxvals = PDLMIN(10, x->nvals);
     EXTEND(sp, maxvals);
     for(i=0; i<maxvals; i++) {