diff --git a/nullability/pointer_nullability_diagnosis.cc b/nullability/pointer_nullability_diagnosis.cc
index da58f1b11..c17dcdfc2 100644
--- a/nullability/pointer_nullability_diagnosis.cc
+++ b/nullability/pointer_nullability_diagnosis.cc
@@ -177,6 +177,30 @@ static const Expr* absl_nullable matchesNonConstCallNullCheck(
                           DynTypedNode::create(*ParentFunction), Ctx));
 }
 
+// Determines if the pointer expression appears inside a lambda via a lambda
+// capture. Handles cases like:
+// - `*p` and `p->x`, where `p` is a captured pointer variable
+// - `*o.p`, where `o` is a captured object with a pointer member `p`
+// Currently does not handle the cases:
+// - `*this->p` and `*p`, where `p` is a pointer member of the enclosing class
+//   and `this` is captured in the lambda.
+static bool isCapturedVariableOrMemberAccess(const Expr* absl_nonnull E) {
+  E = E->IgnoreParenImpCasts();
+
+  // Cases like `*p` and `p->x`, where `p` is captured in the lambda.
+  if (const DeclRefExpr* Variable = dyn_cast<DeclRefExpr>(E))
+    return Variable->refersToEnclosingVariableOrCapture();
+
+  // Cases like `*o.p`, where `o` is an object captured in the lambda.
+  if (const MemberExpr* MemberAccess = dyn_cast<MemberExpr>(E)) {
+    const Expr* Base = MemberAccess->getBase();
+    if (const DeclRefExpr* BaseVariable = dyn_cast<DeclRefExpr>(Base))
+      return BaseVariable->refersToEnclosingVariableOrCapture();
+  }
+
+  return false;
+}
+
 // Diagnoses whether `E` violates the expectation that it is nonnull.
 static SmallVector<PointerNullabilityDiagnostic> diagnoseNonnullExpected(
     const Expr* absl_nonnull E, const Environment& Env, ASTContext& Ctx,
@@ -207,8 +231,7 @@ static SmallVector<PointerNullabilityDiagnostic> diagnoseNonnullExpected(
     Range = CharSourceRange::getTokenRange(E->getSourceRange());
 
   if (const Expr* NullCheck =
-          matchesNonConstCallNullCheck(*E, Ctx, Env.getCurrentFunc());
-      NullCheck != nullptr) {
+          matchesNonConstCallNullCheck(*E, Ctx, Env.getCurrentFunc()))
     return {{
         .Code = PointerNullabilityDiagnostic::ErrorCode::
             ExpectedNonnullWithCheckOnNonConstCall,
@@ -225,12 +248,27 @@ static SmallVector<PointerNullabilityDiagnostic> diagnoseNonnullExpected(
             "that. Or, mark the method as const (if possible, and if it has "
             "zero params).",
     }};
-  }
+
+  Range = getRangeModuloMacros(Range, Ctx);
+
+  if (isCapturedVariableOrMemberAccess(E))
+    return {
+        {.Code = PointerNullabilityDiagnostic::ErrorCode::ExpectedNonnull,
+         .Ctx = DiagCtx,
+         .Range = Range,
+         .Callee = Callee,
+         .ParamName = ParamName,
+         .NoteRange = Range,
+         .NoteMessage =
+             "This pointer is captured and dereferenced in a lambda. If it is "
+             "null-checked outside the lambda, consider capturing the pointee "
+             "by value or reference (possibly with an init-capture). Otherwise "
+             "do a null check inside the lambda body to ensure null safety."}};
 
   return {{
       .Code = PointerNullabilityDiagnostic::ErrorCode::ExpectedNonnull,
       .Ctx = DiagCtx,
-      .Range = getRangeModuloMacros(Range, Ctx),
+      .Range = Range,
       .Callee = Callee,
       .ParamName = ParamName,
   }};