diff --git a/llvm/lib/FileCheck/FileCheck.cpp b/llvm/lib/FileCheck/FileCheck.cpp
--- a/llvm/lib/FileCheck/FileCheck.cpp
+++ b/llvm/lib/FileCheck/FileCheck.cpp
@@ -150,10 +150,9 @@
   (void)MissingFormPrefix;
   assert(!MissingFormPrefix && "missing alternate form prefix");
   APInt ResultValue;
-  bool ParseFailure = StrVal.getAsInteger(Hex ? 16 : 10, ResultValue);
-  if (ParseFailure)
-    return ErrorDiagnostic::get(SM, StrVal,
-                                "unable to represent numeric value");
+  [[maybe_unused]] bool ParseFailure =
+      StrVal.getAsInteger(Hex ? 16 : 10, ResultValue);
+  assert(!ParseFailure && "unable to represent numeric value");
   return toSigned(ResultValue, Negative);
 }
 
diff --git a/llvm/unittests/FileCheck/FileCheckTest.cpp b/llvm/unittests/FileCheck/FileCheckTest.cpp
--- a/llvm/unittests/FileCheck/FileCheckTest.cpp
+++ b/llvm/unittests/FileCheck/FileCheckTest.cpp
@@ -321,7 +321,10 @@
 
   // Wrong casing is not tested because valueFromStringRepr() relies on
   // StringRef's getAsInteger() which does not allow to restrict casing.
-  checkValueFromStringReprFailure(addBasePrefix("G"));
+
+  // Likewise, wrong letter digit for hex value is not tested because it is
+  // only caught by an assert in FileCheck due to getWildcardRegex()
+  // guaranteeing only valid letter digits are used.
 }
 
 TEST_P(ExpressionFormatParameterisedFixture, FormatBoolOperator) {