diff --git a/gcc/cse.c b/gcc/cse.c
index c1c7d0ca27b73c4b944b4719f95fece74e0358d5..08295246c594109e947276051c6776e4cabca4ec 100644
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -1537,6 +1537,17 @@ insert_with_costs (rtx x, struct table_elt *classp, unsigned int hash,
   if (REG_P (x) && REGNO (x) < FIRST_PSEUDO_REGISTER)
     add_to_hard_reg_set (&hard_regs_in_table, GET_MODE (x), REGNO (x));
 
+  /* We cannot allow a duplicate to be entered into the equivalence sets
+     and so we should perform a check before we do any allocations or
+     change the buckets.  */
+  if (classp)
+    {
+      struct table_elt *p;
+      for (p = classp; p; p = p->next_same_value)
+	if (exp_equiv_p (p->exp, x, 1, false))
+	  return p;
+    }
+
   /* Put an element for X into the right hash bucket.  */
 
   elt = free_element_chain;
diff --git a/gcc/testsuite/gcc.target/i386/pr103404.c b/gcc/testsuite/gcc.target/i386/pr103404.c
new file mode 100644
index 0000000000000000000000000000000000000000..66f33645301db09503fc0977fd0f061a19e56ea5
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr103404.c
@@ -0,0 +1,32 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-Og -fcse-follow-jumps -fno-dce -fno-early-inlining -fgcse -fharden-conditional-branches -frerun-cse-after-loop -fno-tree-ccp -mavx5124fmaps -std=c99 -w" } */
+
+typedef unsigned __attribute__((__vector_size__ (4))) U;
+typedef unsigned __attribute__((__vector_size__ (16))) V;
+typedef unsigned __attribute__((__vector_size__ (64))) W;
+
+int x, y;
+
+V v;
+W w;
+
+inline
+int bar (U a)
+{
+  a |= x;
+  W k =
+    __builtin_shufflevector (v, 5 / a,
+			     2, 4, 0, 2, 4, 1, 0, 1,
+			     1, 2, 1, 3, 0, 4, 4, 0);
+  w = k;
+  y = 0;
+}
+
+int
+foo ()
+{
+  bar ((U){0xffffffff});
+  for (unsigned i; i < sizeof (foo);)
+    ;
+}
+