diff --git a/build/clang-plugin/RefCountedInsideLambdaChecker.cpp b/build/clang-plugin/RefCountedInsideLambdaChecker.cpp
index 8a95b761de27..03709bc25879 100644
--- a/build/clang-plugin/RefCountedInsideLambdaChecker.cpp
+++ b/build/clang-plugin/RefCountedInsideLambdaChecker.cpp
@@ -36,6 +36,18 @@ void RefCountedInsideLambdaChecker::emitDiagnostics(SourceLocation Loc,
   diag(Loc, "Please consider using a smart pointer", DiagnosticIDs::Note);
 }
 
+static bool IsKnownLive(const VarDecl *Var) {
+  const Stmt *Init = Var->getInit();
+  if (!Init) {
+    return false;
+  }
+  if (auto *Call = dyn_cast<CallExpr>(Init)) {
+    const FunctionDecl *Callee = Call->getDirectCallee();
+    return Callee && Callee->getName() == "MOZ_KnownLive";
+  }
+  return false;
+}
+
 void RefCountedInsideLambdaChecker::check(
     const MatchFinder::MatchResult &Result) {
   static DenseSet<const CXXRecordDecl *> CheckedDecls;
@@ -107,11 +119,11 @@ void RefCountedInsideLambdaChecker::check(
   // pointers.
   for (const LambdaCapture &Capture : Lambda->captures()) {
     if (Capture.capturesVariable()) {
-      QualType Pointee = Capture.getCapturedVar()->getType()->getPointeeType();
-
-      if (!Pointee.isNull() && isClassRefCounted(Pointee)) {
-        emitDiagnostics(Capture.getLocation(),
-                        Capture.getCapturedVar()->getName(), Pointee);
+      const VarDecl *Var = Capture.getCapturedVar();
+      QualType Pointee = Var->getType()->getPointeeType();
+      if (!Pointee.isNull() && isClassRefCounted(Pointee) &&
+          !IsKnownLive(Var)) {
+        emitDiagnostics(Capture.getLocation(), Var->getName(), Pointee);
         return;
       }
     }
diff --git a/build/clang-plugin/tests/TestNoRefcountedInsideLambdas.cpp b/build/clang-plugin/tests/TestNoRefcountedInsideLambdas.cpp
index 4b4b814751cc..aedc5af096cd 100644
--- a/build/clang-plugin/tests/TestNoRefcountedInsideLambdas.cpp
+++ b/build/clang-plugin/tests/TestNoRefcountedInsideLambdas.cpp
@@ -1,3 +1,5 @@
+#include <mozilla/StaticAnalysisFunctions.h>
+
 #include <functional>
 #define MOZ_STRONG_REF
 #define MOZ_IMPLICIT __attribute__((annotate("moz_implicit")))
@@ -667,6 +669,9 @@ R::privateMethod() {
     privateMethod();
   });
 
+  std::function<void()>(
+      [instance = MOZ_KnownLive(this)]() { instance->privateMethod(); });
+
   // It should be OK to go through `this` if we have captured a reference to it.
   std::function<void()>([this, self]() {
     this->method();
diff --git a/mfbt/StaticAnalysisFunctions.h b/mfbt/StaticAnalysisFunctions.h
index 93e6f678455a..b073055c05fd 100644
--- a/mfbt/StaticAnalysisFunctions.h
+++ b/mfbt/StaticAnalysisFunctions.h
@@ -13,6 +13,7 @@
 #  endif
 #  define MOZ_CONSTEXPR
 #else  // __cplusplus
+#  include "mozilla/Attributes.h"
 #  define MOZ_CONSTEXPR constexpr
 #endif
 /*