diff --git a/gcc/testsuite/gcc.dg/torture/pr126650.c b/gcc/testsuite/gcc.dg/torture/pr126650.c
new file mode 100644
index 00000000000..166705d9cfe
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr126650.c
@@ -0,0 +1,35 @@
+/* { dg-do run } */
+
+#include <stdarg.h>
+#include <stdlib.h>
+
+long a;
+
+void __attribute__((noipa)) foo (int n, ...)
+{
+  va_list list;
+  va_start (list, n);
+  int val = va_arg (list, int);
+  if (val != -64)
+    abort ();
+  va_end (list);
+}
+
+int main()
+{
+  struct b {
+    int : 7;
+    int : 2;
+    int : 6;
+    int : 3;
+    int c : 7;
+  };
+  union {
+    int d;
+    struct b bf;
+    char e[4];
+  } f;
+  f.d = a;
+  f.e[3] = 7;
+  foo (1, f.bf.c);
+}
diff --git a/gcc/tree-affine.cc b/gcc/tree-affine.cc
index b5b7249c675..181fd6fb33c 100644
--- a/gcc/tree-affine.cc
+++ b/gcc/tree-affine.cc
@@ -1030,10 +1030,11 @@ get_inner_reference_aff (tree ref, aff_tree *addr, poly_widest_int *size)
       aff_combination_add (addr, &tmp);
     }
 
-  aff_combination_const (&tmp, sizetype, bits_to_bytes_round_down (bitpos));
+  poly_int64 bytepos = bits_to_bytes_round_down (bitpos);
+  aff_combination_const (&tmp, sizetype, bytepos);
   aff_combination_add (addr, &tmp);
 
-  *size = bits_to_bytes_round_up (bitsize);
+  *size = bits_to_bytes_round_up (bitpos + bitsize) - bytepos;
 
   return base;
 }