diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index cd4cee631568..9a4a69c90528 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2264,9 +2264,9 @@ static unsigned ComputeNumSignBitsImpl(const Value *V, unsigned Depth,
     // ashr X, C   -> adds C sign bits.  Vectors too.
     const APInt *ShAmt;
     if (match(U->getOperand(1), m_APInt(ShAmt))) {
-      unsigned ShAmtLimited = ShAmt->getZExtValue();
-      if (ShAmtLimited >= TyBits)
+      if (ShAmt->uge(TyBits))
         break;  // Bad shift.
+      unsigned ShAmtLimited = ShAmt->getZExtValue();
       Tmp += ShAmtLimited;
       if (Tmp > TyBits) Tmp = TyBits;
     }
@@ -2277,9 +2277,9 @@ static unsigned ComputeNumSignBitsImpl(const Value *V, unsigned Depth,
     if (match(U->getOperand(1), m_APInt(ShAmt))) {
       // shl destroys sign bits.
       Tmp = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
+      if (ShAmt->uge(TyBits) ||      // Bad shift.
+          ShAmt->uge(Tmp)) break;    // Shifted all sign bits out.
       Tmp2 = ShAmt->getZExtValue();
-      if (Tmp2 >= TyBits ||      // Bad shift.
-          Tmp2 >= Tmp) break;    // Shifted all sign bits out.
       return Tmp - Tmp2;
     }
     break;
diff --git a/llvm/test/Transforms/InstCombine/udiv-simplify.ll b/llvm/test/Transforms/InstCombine/udiv-simplify.ll
index 885a901a7d30..1794e26d389d 100644
--- a/llvm/test/Transforms/InstCombine/udiv-simplify.ll
+++ b/llvm/test/Transforms/InstCombine/udiv-simplify.ll
@@ -62,3 +62,24 @@ define i32 @PR30366(i1 %a) {
   %d = udiv i32 %z, zext (i16 shl (i16 1, i16 ptrtoint ([1 x i16]* @b to i16)) to i32)
   ret i32 %d
 }
+
+; OSS-Fuzz #4857
+; https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=4857
+define i177 @ossfuzz_4857(i177 %X, i177 %Y) {
+; CHECK-LABEL: @ossfuzz_4857(
+; CHECK-NEXT:    store i1 false, i1* undef, align 1
+; CHECK-NEXT:    ret i177 0
+;
+  %B5 = udiv i177 %Y, -1
+  %B4 = add i177 %B5, -1
+  %B2 = add i177 %B4, -1
+  %B6 = mul i177 %B5, %B2
+  %B3 = add i177 %B2, %B2
+  %B9 = xor i177 %B4, %B3
+  %B13 = ashr i177 %Y, %B2
+  %B22 = add i177 %B9, %B13
+  %B1 = udiv i177 %B5, %B6
+  %C9 = icmp ult i177 %Y, %B22
+  store i1 %C9, i1* undef
+  ret i177 %B1
+}