diff --git a/src/nunit.analyzers.tests/DiagnosticSuppressors/DereferencePossiblyNullReferenceSuppressorTests.cs b/src/nunit.analyzers.tests/DiagnosticSuppressors/DereferencePossiblyNullReferenceSuppressorTests.cs
index a894a85b..7fe64b2a 100644
--- a/src/nunit.analyzers.tests/DiagnosticSuppressors/DereferencePossiblyNullReferenceSuppressorTests.cs
+++ b/src/nunit.analyzers.tests/DiagnosticSuppressors/DereferencePossiblyNullReferenceSuppressorTests.cs
@@ -1032,5 +1032,27 @@ public HasString(string? inner)
                 ExpectedDiagnostic.Create(DereferencePossiblyNullReferenceSuppressor.SuppressionDescriptors["CS8603"]),
                 testCode);
         }
+
+        [Test]
+        public void TestIssue739FullyQualified()
+        {
+            var testCode = TestUtility.WrapMethodInClassNamespaceAndAddUsings(@"
+                [Test]
+                public void T()
+                {
+                    object? x = null;
+                    NUnit.Framework.Assert.That(x, Is.Not.Null);
+                    M(x);
+                }
+
+                void M(object o)
+                {
+                }
+            ");
+
+            RoslynAssert.Suppressed(suppressor,
+                ExpectedDiagnostic.Create(DereferencePossiblyNullReferenceSuppressor.SuppressionDescriptors["CS8604"]),
+                testCode);
+        }
     }
 }
diff --git a/src/nunit.analyzers/Helpers/AssertHelper.cs b/src/nunit.analyzers/Helpers/AssertHelper.cs
index 6089cde8..f5387876 100644
--- a/src/nunit.analyzers/Helpers/AssertHelper.cs
+++ b/src/nunit.analyzers/Helpers/AssertHelper.cs
@@ -144,20 +144,33 @@ private static bool IsAssert(ExpressionSyntax? expression,
                                      [NotNullWhen(true)] out ArgumentListSyntax? argumentList)
         {
             if (expression is InvocationExpressionSyntax invocationExpression &&
-                invocationExpression.Expression is MemberAccessExpressionSyntax memberAccessExpression &&
-                memberAccessExpression.Expression is IdentifierNameSyntax identifierName &&
-                isNameOfAssert(identifierName.Identifier.Text))
+                invocationExpression.Expression is MemberAccessExpressionSyntax memberAccessExpression)
             {
-                member = memberAccessExpression.Name.Identifier.Text;
-                argumentList = invocationExpression.ArgumentList;
-                return true;
-            }
-            else
-            {
-                member = string.Empty;
-                argumentList = null;
-                return false;
+                SimpleNameSyntax? className = GetClassName(memberAccessExpression);
+
+                if (className is not null &&
+                    isNameOfAssert(className.Identifier.Text))
+                {
+                    member = memberAccessExpression.Name.Identifier.Text;
+                    argumentList = invocationExpression.ArgumentList;
+                    return true;
+                }
             }
+
+            member = string.Empty;
+            argumentList = null;
+            return false;
+        }
+
+        private static SimpleNameSyntax? GetClassName(MemberAccessExpressionSyntax memberAccessExpression)
+        {
+            if (memberAccessExpression.Expression is MemberAccessExpressionSyntax nestedMemberAccessExpression)
+                return nestedMemberAccessExpression.Name;
+
+            if (memberAccessExpression.Expression is IdentifierNameSyntax identifierName)
+                return identifierName;
+
+            return null;
         }
     }
 }