diff --git a/src/pmc/NumMatrix2D.pmc b/src/pmc/NumMatrix2D.pmc
index 3eac8c6..18ed156 100644
--- a/src/pmc/NumMatrix2D.pmc
+++ b/src/pmc/NumMatrix2D.pmc
@@ -53,7 +53,8 @@ pmclass NumMatrix2D auto_attrs {
         y_size = attrs->y;
         GET_INDICES_FROM_KEY(INTERP, key, x, y);
         if (x >= x_size || y >= y_size)
-            Parrot_ex_throw_from_c_args(INTERP, ...);
+            Parrot_ex_throw_from_c_args(INTERP, NULL, EXCEPTION_OUT_OF_BOUNDS,
+                "NumMatrix2d: indices out of bounds");
         return ITEM_XY_ROWMAJOR(attrs->storage, x_size, y_size, x, y);
     }
 
diff --git a/src/pmc/NumMatrix2D.pmc~ b/src/pmc/NumMatrix2D.pmc~
index 475c724..18ed156 100644
--- a/src/pmc/NumMatrix2D.pmc~
+++ b/src/pmc/NumMatrix2D.pmc~
@@ -15,8 +15,26 @@
 #define INDEX_MAX(a, b) (((a) >= (b))?(a):(b))
 
 void
-resize_matrix(PARROT_INTERP, PMC * self, INTVAL x, INTVAL y)
+resize_matrix(PARROT_INTERP, PMC * self, INTVAL new_x, INTVAL new_y)
 {
+    Parrot_NumMatrix2D_attributes * const attrs = PARROT_NUMMATRIX2D(self);
+    const INTVAL old_x = attrs->x;
+    const INTVAL old_y = attrs->y;
+    const INTVAL newsize = new_x * new_y;
+    FLOATVAL * new_s = (FLOATVAL *)calloc(newsize * sizeof (FLOATVAL));
+    FLOATVAL * old_s = attrs->storage;
+    const INTVAL min_x = INDEX_MIN(old_x, new_x);
+    const INTVAL min_y = INDEX_MIN(old_y, new_y);
+    INTVAL i, j;
+    for (i = 0; i < min_x; i++) {
+        for (j = 0; j < min_y; j++) {
+            ITEM_XY_ROWMAJOR(new_s, new_x, new_y, i, j) =
+                ITEM_XY_ROWMAJOR(old_s, old_x, old_y, i, j);
+        }
+    }
+    attrs->storage = new_s;
+    free(old_s);
+}
 
 
 pmclass NumMatrix2D auto_attrs {
@@ -35,7 +53,8 @@ pmclass NumMatrix2D auto_attrs {
         y_size = attrs->y;
         GET_INDICES_FROM_KEY(INTERP, key, x, y);
         if (x >= x_size || y >= y_size)
-            Parrot_ex_throw_from_c_args(INTERP, ...);
+            Parrot_ex_throw_from_c_args(INTERP, NULL, EXCEPTION_OUT_OF_BOUNDS,
+                "NumMatrix2d: indices out of bounds");
         return ITEM_XY_ROWMAJOR(attrs->storage, x_size, y_size, x, y);
     }
 
@@ -49,4 +68,4 @@ pmclass NumMatrix2D auto_attrs {
             resize_matrix(INTERP, SELF, x, y);
         ITEM_XY_ROWMAJOR(attrs->storage, x_size, y_size, x, y) = value;
     }
-}
\ No newline at end of file
+}