diff --git a/NullabilityInference.Tests/FlowTests.cs b/NullabilityInference.Tests/FlowTests.cs
index f6c62d7..7cc60be 100644
--- a/NullabilityInference.Tests/FlowTests.cs
+++ b/NullabilityInference.Tests/FlowTests.cs
@@ -259,5 +259,25 @@ public bool TryGet(int i, [Attr] out string? name)
                 expectedProgram: program.Replace("[Attr]", "[NotNullWhen(true)]").Replace("[using]", "using System.Diagnostics.CodeAnalysis;"),
                 inputProgram: program.Replace("[Attr] ", "").Replace("[using]", ""));
         }
+
+        [Fact]
+        public void UseNotNullIfNotNull()
+        {
+            string program = @"
+using System.Diagnostics.CodeAnalysis;
+class Program
+{
+	public void Test()
+    {
+		string a = Identitity(string.Empty);
+		string? b = Identitity(null);
+    }
+
+#nullable enable
+	[return: NotNullIfNotNull(""input"")]
+    public static string? Identitity(string? input) => input;
+}";
+            AssertNullabilityInference(program, program);
+        }
     }
 }
diff --git a/NullabilityInference/EdgeBuildingOperationVisitor.cs b/NullabilityInference/EdgeBuildingOperationVisitor.cs
index e35e782..c92ff37 100644
--- a/NullabilityInference/EdgeBuildingOperationVisitor.cs
+++ b/NullabilityInference/EdgeBuildingOperationVisitor.cs
@@ -889,9 +889,14 @@ public override TypeWithNode VisitInvocation(IInvocationOperation operation, Edg
             }
             methodTypeArgNodes = ExtendMethodTypeArguments(targetMethod, methodTypeArgNodes);
             var substitution = new TypeSubstitution(classTypeArgNodes, methodTypeArgNodes);
-            HandleArguments(substitution, operation.Arguments, invocationContext: argument);
+            var argumentTypes = HandleArguments(substitution, operation.Arguments, invocationContext: argument);
             var returnType = typeSystem.GetSymbolType(targetMethod.OriginalDefinition);
             returnType = returnType.WithSubstitution(targetMethod.ReturnType, substitution);
+
+            if (typeSystem.GetNotNullIfNotNullParam(operation.TargetMethod.OriginalDefinition) is { } notNullParam) {
+                returnType = returnType.WithNode(argumentTypes[notNullParam.Ordinal].Node);
+            }
+
             return returnType;
         }
 
@@ -967,8 +972,9 @@ private void HandleMethodGroup(IMethodReferenceOperation operation, TypeWithNode
             _ => null,
         };
 
-        private void HandleArguments(TypeSubstitution substitution, ImmutableArray<IArgumentOperation> arguments, EdgeBuildingContext invocationContext)
+        private List<TypeWithNode> HandleArguments(TypeSubstitution substitution, ImmutableArray<IArgumentOperation> arguments, EdgeBuildingContext invocationContext)
         {
+            List<TypeWithNode> argumentTypes = new List<TypeWithNode>();
             Action? afterCall = null;
             FlowState? flowStateOnTrue = null;
             FlowState? flowStateOnFalse = null;
@@ -977,6 +983,7 @@ private void HandleArguments(TypeSubstitution substitution, ImmutableArray<IArgu
                 var parameterType = typeSystem.GetSymbolType(param);
                 bool isLValue = param.RefKind == RefKind.Ref || param.RefKind == RefKind.Out;
                 var argumentType = Visit(arg.Value, isLValue ? EdgeBuildingContext.LValue : EdgeBuildingContext.Normal);
+                argumentTypes.Add(argumentType);
                 // Create an assignment edge from argument to parameter.
                 // We use the parameter's original type + substitution so that a type parameter `T` appearing in
                 // multiple parameters uses the same nullability nodes for all occurrences.
@@ -1024,6 +1031,7 @@ private void HandleArguments(TypeSubstitution substitution, ImmutableArray<IArgu
                 Debug.Assert(flowStateOnTrue == null && flowStateOnFalse == null);
                 Debug.Assert(flowStateReturnedOnTrue == null && flowStateReturnedOnFalse == null);
             }
+            return argumentTypes;
         }
 
         private TypeWithNode currentObjectCreationType;
diff --git a/NullabilityInference/TypeSystem.cs b/NullabilityInference/TypeSystem.cs
index 5d7ae2f..72b4657 100644
--- a/NullabilityInference/TypeSystem.cs
+++ b/NullabilityInference/TypeSystem.cs
@@ -608,5 +608,20 @@ internal void CreateTypeEdge(TypeWithNode source, TypeWithNode target, TypeSubst
                 return edge;
             }
         }
+
+        internal IParameterSymbol? GetNotNullIfNotNullParam(IMethodSymbol method)
+        {
+            foreach (var attr in method.GetReturnTypeAttributes()) {
+                if (attr.AttributeClass?.GetFullName() == "System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute"
+                    && attr.ConstructorArguments.Length == 1
+                    && attr.ConstructorArguments[0].Value is string parameterName) {
+                    foreach (var p in method.Parameters) {
+                        if (p.Name == parameterName)
+                            return p;
+                    }
+                }
+            }
+            return null;
+        }
     }
 }