diff --git a/clang-tools-extra/clang-tidy/bugprone/NotNullTerminatedResultCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/NotNullTerminatedResultCheck.cpp
index 3dd0a50b70c8a..ca85168ffce0b 100644
--- a/clang-tools-extra/clang-tidy/bugprone/NotNullTerminatedResultCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/NotNullTerminatedResultCheck.cpp
@@ -309,10 +309,9 @@ static void lengthExprHandle(const Expr *LengthExpr,
   // Try to obtain an 'IntegerLiteral' and adjust it.
   if (!IsMacroDefinition) {
     if (const auto *LengthIL = dyn_cast<IntegerLiteral>(LengthExpr)) {
-      size_t NewLength = LengthIL->getValue().getZExtValue() +
-                         (LengthHandle == LengthHandleKind::Increase
-                              ? (isInjectUL(Result) ? 1UL : 1)
-                              : -1);
+      uint64_t NewLength =
+          LengthIL->getValue().getZExtValue() +
+          (LengthHandle == LengthHandleKind::Increase ? 1 : -1);
 
       const auto NewLengthFix = FixItHint::CreateReplacement(
           LengthIL->getSourceRange(),
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 11f2ae993629f..6c104bb612a47 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -276,6 +276,7 @@ Changes in existing checks
 
 - Improved :doc:`bugprone-not-null-terminated-result
   <clang-tidy/checks/bugprone/not-null-terminated-result>` check by fixing
+  bogus fix-its for ``strncmp`` and ``wcsncmp`` on Windows and
   a crash caused by certain value-dependent expressions.
 
 - Improved :doc:`bugprone-reserved-identifier
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/not-null-terminated-result-strlen.c b/clang-tools-extra/test/clang-tidy/checkers/bugprone/not-null-terminated-result-strlen.c
index dccf4ed799499..ca86986f4afce 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/not-null-terminated-result-strlen.c
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/not-null-terminated-result-strlen.c
@@ -1,11 +1,6 @@
 // RUN: %check_clang_tidy %s bugprone-not-null-terminated-result %t -- \
 // RUN: -- -I %S/Inputs/not-null-terminated-result
 
-// FIXME: Something wrong with the APInt un/signed conversion on Windows:
-// in 'strncmp(str6, "string", 7);' it tries to inject '4294967302' as length.
-
-// UNSUPPORTED: system-windows
-
 #include "not-null-terminated-result-c.h"
 
 #define __STDC_LIB_EXT1__ 1
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/not-null-terminated-result-wcslen.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/not-null-terminated-result-wcslen.cpp
index 8047db3f19969..688e41471d867 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/not-null-terminated-result-wcslen.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/not-null-terminated-result-wcslen.cpp
@@ -1,11 +1,6 @@
 // RUN: %check_clang_tidy -std=c++11-or-later %s bugprone-not-null-terminated-result %t -- \
 // RUN: -- -I %S/Inputs/not-null-terminated-result
 
-// FIXME: Something wrong with the APInt un/signed conversion on Windows:
-// in 'wcsncmp(wcs6, L"string", 7);' it tries to inject '4294967302' as length.
-
-// UNSUPPORTED: system-windows
-
 #include "not-null-terminated-result-cxx.h"
 
 #define __STDC_LIB_EXT1__ 1