diff --git a/gcc/gimple-range-cache.cc b/gcc/gimple-range-cache.cc
index ce5a0c8155e6..9848d140242f 100644
--- a/gcc/gimple-range-cache.cc
+++ b/gcc/gimple-range-cache.cc
@@ -1235,6 +1235,13 @@ ranger_cache::fill_block_cache (tree name, basic_block bb, basic_block def_bb)
 	      if (!m_gori.has_edge_range_p (equiv_name))
 		continue;
 
+	      // PR 108139. It is hazardous to assume an equivalence with
+	      // a PHI is the same value.  The PHI may be an equivalence
+	      // via UNDEFINED arguments which is really a one way equivalence.
+	      // PHIDEF == name, but name may not be == PHIDEF.
+	      if (is_a<gphi *> (SSA_NAME_DEF_STMT (equiv_name)))
+		continue;
+
 	      // Check if the equiv definition dominates this block
 	      if (equiv_bb == bb ||
 		  (equiv_bb && !dominated_by_p (CDI_DOMINATORS, bb, equiv_bb)))
diff --git a/gcc/testsuite/gcc.dg/pr108139.c b/gcc/testsuite/gcc.dg/pr108139.c
new file mode 100644
index 000000000000..6f224e3ce629
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr108139.c
@@ -0,0 +1,18 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O1 -ftree-vrp -fdump-tree-vrp" } */
+
+int a, b;
+int main() {
+  int c;
+  if (a > 1)
+    a++;
+  while (a)
+    if (c == b)
+      c = a;
+  return 0;
+}
+
+
+/* { dg-final { scan-tree-dump-not "Folding predicate" "vrp2" } } */
+
+