diff --git a/lib/Analysis/MemoryBuiltins.cpp b/lib/Analysis/MemoryBuiltins.cpp
index 4833b52..c0cc27b 100644
--- a/lib/Analysis/MemoryBuiltins.cpp
+++ b/lib/Analysis/MemoryBuiltins.cpp
@@ -506,6 +506,10 @@
 }
 
 SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {
+  // ignore malformed self-looping selects
+  if (I.getTrueValue() == &I || I.getFalseValue() == &I)
+    return unknown();
+
   SizeOffsetType TrueSide  = compute(I.getTrueValue());
   SizeOffsetType FalseSide = compute(I.getFalseValue());
   if (bothKnown(TrueSide) && bothKnown(FalseSide) && TrueSide == FalseSide)
@@ -711,6 +715,10 @@
 }
 
 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitSelectInst(SelectInst &I) {
+  // ignore malformed self-looping selects
+  if (I.getTrueValue() == &I || I.getFalseValue() == &I)
+    return unknown();
+
   SizeOffsetEvalType TrueSide  = compute_(I.getTrueValue());
   SizeOffsetEvalType FalseSide = compute_(I.getFalseValue());
 
diff --git a/test/Transforms/InstCombine/objsize.ll b/test/Transforms/InstCombine/objsize.ll
index 1818d89..dbb0ffc 100644
--- a/test/Transforms/InstCombine/objsize.ll
+++ b/test/Transforms/InstCombine/objsize.ll
@@ -219,3 +219,22 @@
 ; CHECK: ret i32 8
   ret i32 %1
 }
+
+; CHECK: @PR13390
+define i32 @PR13390(i1 %bool, i8* %a) {
+entry:
+  %cond = or i1 %bool, true
+  br i1 %cond, label %return, label %xpto
+
+xpto:
+  %select = select i1 %bool, i8* %select, i8* %a
+  %select2 = select i1 %bool, i8* %a, i8* %select2
+  %0 = tail call i32 @llvm.objectsize.i32(i8* %select, i1 true)
+  %1 = tail call i32 @llvm.objectsize.i32(i8* %select2, i1 true)
+  %2 = add i32 %0, %1
+; CHECK: ret i32 undef
+  ret i32 %2
+
+return:
+  ret i32 42
+}