diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index b5286e8..bc0dffc 100644
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -551,7 +551,7 @@
 
 
   if (Opc == Instruction::And && DL) {
-    unsigned BitWidth = DL->getTypeSizeInBits(Op0->getType());
+    unsigned BitWidth = DL->getTypeSizeInBits(Op0->getType()->getScalarType());
     APInt KnownZero0(BitWidth, 0), KnownOne0(BitWidth, 0);
     APInt KnownZero1(BitWidth, 0), KnownOne1(BitWidth, 0);
     ComputeMaskedBits(Op0, KnownZero0, KnownOne0, DL);
diff --git a/test/Transforms/InstSimplify/2013-04-19-ConstantFoldingCrash.ll b/test/Transforms/InstSimplify/2013-04-19-ConstantFoldingCrash.ll
new file mode 100644
index 0000000..1647517
--- /dev/null
+++ b/test/Transforms/InstSimplify/2013-04-19-ConstantFoldingCrash.ll
@@ -0,0 +1,9 @@
+; RUN: opt < %s -instsimplify
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+
+; PR15791
+define <2 x i64> @test1() {
+  %a = and <2 x i64> undef, bitcast (<4 x i32> <i32 undef, i32 undef, i32 undef, i32 2147483647> to <2 x i64>)
+  ret <2 x i64> %a
+}