diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index ffcf97c62e43..09687d8909da 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -543,6 +543,7 @@ static bool LinearizeExprTree(BinaryOperator *I,
         // Update the number of paths to the leaf.
         IncorporateWeight(It->second, Weight, Opcode);
 
+#if 0   // TODO: Re-enable once PR13021 is fixed.
         // The leaf already has one use from inside the expression.  As we want
         // exactly one such use, drop this new use of the leaf.
         assert(!Op->hasOneUse() && "Only one use, but we got here twice!");
@@ -559,6 +560,7 @@ static bool LinearizeExprTree(BinaryOperator *I,
           Leaves.erase(It);
           continue;
         }
+#endif
 
         // If we still have uses that are not accounted for by the expression
         // then it is not safe to modify the value.
diff --git a/llvm/test/Transforms/Reassociate/2012-05-08-UndefLeak.ll b/llvm/test/Transforms/Reassociate/2012-05-08-UndefLeak.ll
index 1e522e616018..2f5a53e0ce46 100644
--- a/llvm/test/Transforms/Reassociate/2012-05-08-UndefLeak.ll
+++ b/llvm/test/Transforms/Reassociate/2012-05-08-UndefLeak.ll
@@ -1,6 +1,8 @@
 ; RUN: opt < %s -reassociate -S | FileCheck %s
 ; PR12169
 ; PR12764
+; XFAIL: *
+; Transform disabled until PR13021 is fixed.
 
 define i64 @f(i64 %x0) {
 ; CHECK: @f
diff --git a/llvm/test/Transforms/Reassociate/mightymul.ll b/llvm/test/Transforms/Reassociate/mightymul.ll
new file mode 100644
index 000000000000..cfbc485ffa03
--- /dev/null
+++ b/llvm/test/Transforms/Reassociate/mightymul.ll
@@ -0,0 +1,35 @@
+; RUN: opt < %s -reassociate
+; PR13021
+
+define i32 @foo(i32 %x) {
+  %t0 = mul i32 %x, %x
+  %t1 = mul i32 %t0, %t0
+  %t2 = mul i32 %t1, %t1
+  %t3 = mul i32 %t2, %t2
+  %t4 = mul i32 %t3, %t3
+  %t5 = mul i32 %t4, %t4
+  %t6 = mul i32 %t5, %t5
+  %t7 = mul i32 %t6, %t6
+  %t8 = mul i32 %t7, %t7
+  %t9 = mul i32 %t8, %t8
+  %t10 = mul i32 %t9, %t9
+  %t11 = mul i32 %t10, %t10
+  %t12 = mul i32 %t11, %t11
+  %t13 = mul i32 %t12, %t12
+  %t14 = mul i32 %t13, %t13
+  %t15 = mul i32 %t14, %t14
+  %t16 = mul i32 %t15, %t15
+  %t17 = mul i32 %t16, %t16
+  %t18 = mul i32 %t17, %t17
+  %t19 = mul i32 %t18, %t18
+  %t20 = mul i32 %t19, %t19
+  %t21 = mul i32 %t20, %t20
+  %t22 = mul i32 %t21, %t21
+  %t23 = mul i32 %t22, %t22
+  %t24 = mul i32 %t23, %t23
+  %t25 = mul i32 %t24, %t24
+  %t26 = mul i32 %t25, %t25
+  %t27 = mul i32 %t26, %t26
+  %t28 = mul i32 %t27, %t27
+  ret i32 %t28
+}