diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index f6cc431656b8..5867d65e7e41 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -782,7 +782,9 @@ Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilder<> &B) {
   // memchr("\r\n", C, 2) != nullptr -> (C & ((1 << '\r') | (1 << '\n'))) != 0
   //   after bounds check.
   if (!CharC && !Str.empty() && isOnlyUsedInZeroEqualityComparison(CI)) {
-    unsigned char Max = *std::max_element(Str.begin(), Str.end());
+    unsigned char Max =
+        *std::max_element(reinterpret_cast<const unsigned char *>(Str.begin()),
+                          reinterpret_cast<const unsigned char *>(Str.end()));
 
     // Make sure the bit field we're about to create fits in a register on the
     // target.
diff --git a/llvm/test/Transforms/InstCombine/memchr.ll b/llvm/test/Transforms/InstCombine/memchr.ll
index 6783249877d3..216dba874ccb 100644
--- a/llvm/test/Transforms/InstCombine/memchr.ll
+++ b/llvm/test/Transforms/InstCombine/memchr.ll
@@ -9,6 +9,7 @@ target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f3
 @newlines = constant [3 x i8] c"\0D\0A\00"
 @single = constant [2 x i8] c"\1F\00"
 @spaces = constant [4 x i8] c" \0D\0A\00"
+@negative = constant [3 x i8] c"\FF\FE\00"
 @chp = global i8* zeroinitializer
 
 declare i8* @memchr(i8*, i32, i32)
@@ -186,3 +187,14 @@ define i1 @test14(i32 %C) {
   %cmp = icmp ne i8* %dst, null
   ret i1 %cmp
 }
+
+define i1 @test15(i32 %C) {
+; CHECK-LABEL: @test15
+; CHECK-NEXT: %dst = call i8* @memchr(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @negative, i32 0, i32 0), i32 %C, i32 3)
+; CHECK-NEXT: %cmp = icmp ne i8* %dst, null
+; CHECK-NEXT: ret i1 %cmp
+
+  %dst = call i8* @memchr(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @negative, i64 0, i64 0), i32 %C, i32 3)
+  %cmp = icmp ne i8* %dst, null
+  ret i1 %cmp
+}