diff --git a/llvm/include/llvm/ADT/APInt.h b/llvm/include/llvm/ADT/APInt.h
--- a/llvm/include/llvm/ADT/APInt.h
+++ b/llvm/include/llvm/ADT/APInt.h
@@ -1458,10 +1458,8 @@
   /// uint64_t. The bitwidth must be <= 64 or the value must fit within a
   /// uint64_t. Otherwise an assertion will result.
   uint64_t getZExtValue() const {
-    if (isSingleWord()) {
-      assert(BitWidth && "zero width values not allowed");
+    if (isSingleWord())
       return U.VAL;
-    }
     assert(getActiveBits() <= 64 && "Too many bits for uint64_t");
     return U.pVal[0];
   }
diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -3054,6 +3054,9 @@
   EXPECT_EQ(0U, APInt(4, 3).trunc(0).getBitWidth());
   EXPECT_TRUE(ZW.isAllOnes());
 
+  // Zero extension.
+  EXPECT_EQ(0U, ZW.getZExtValue());
+
   SmallString<42> STR;
   ZW.toStringUnsigned(STR);
   EXPECT_EQ("0", STR);