diff --git a/src/Stacktrace.php b/src/Stacktrace.php
index cf0e68e46..370bfe9ae 100644
--- a/src/Stacktrace.php
+++ b/src/Stacktrace.php
@@ -115,7 +115,7 @@ public function addFrame(string $file, int $line, array $backtraceFrame): void
             $line = (int) $matches[2];
         }
 
-        if (isset($backtraceFrame['class'])) {
+        if (isset($backtraceFrame['class']) && isset($backtraceFrame['function'])) {
             $functionName = sprintf('%s::%s', $backtraceFrame['class'], $backtraceFrame['function']);
         } elseif (isset($backtraceFrame['function'])) {
             $functionName = $backtraceFrame['function'];
diff --git a/tests/Fixtures/backtraces/anonymous_frame.json b/tests/Fixtures/backtraces/anonymous_frame.json
index 84eaa9898..2f450a5db 100644
--- a/tests/Fixtures/backtraces/anonymous_frame.json
+++ b/tests/Fixtures/backtraces/anonymous_frame.json
@@ -12,4 +12,4 @@
             "function": "call_user_func"
         }
     ]
-}
\ No newline at end of file
+}
diff --git a/tests/Fixtures/backtraces/exception.json b/tests/Fixtures/backtraces/exception.json
index 543157330..f371c73e5 100644
--- a/tests/Fixtures/backtraces/exception.json
+++ b/tests/Fixtures/backtraces/exception.json
@@ -15,4 +15,4 @@
             "function": "crashyFunction"
         }
     ]
-}
\ No newline at end of file
+}
diff --git a/tests/Fixtures/frames/missing_function_key.json b/tests/Fixtures/frames/missing_function_key.json
new file mode 100644
index 000000000..898b752e7
--- /dev/null
+++ b/tests/Fixtures/frames/missing_function_key.json
@@ -0,0 +1,5 @@
+{
+    "file": "path/to/file",
+    "line": 12,
+    "class": "TestClass"
+}
diff --git a/tests/StacktraceTest.php b/tests/StacktraceTest.php
index 7c5bd2849..08222be4a 100644
--- a/tests/StacktraceTest.php
+++ b/tests/StacktraceTest.php
@@ -39,15 +39,17 @@ public function testGetFramesAndToArray(): void
     {
         $stacktrace = new Stacktrace($this->options, $this->serializer, $this->representationSerializer);
 
-        $stacktrace->addFrame('path/to/file', 1, ['file' => 'path/to/file', 'line' => 1, 'function' => 'test_function']);
-        $stacktrace->addFrame('path/to/file', 2, ['file' => 'path/to/file', 'line' => 2, 'function' => 'test_function', 'class' => 'TestClass']);
+        $stacktrace->addFrame('path/to/file', 1, ['file' => 'path/to/file', 'line' => 1, 'class' => 'TestClass']);
+        $stacktrace->addFrame('path/to/file', 2, ['file' => 'path/to/file', 'line' => 2, 'function' => 'test_function']);
+        $stacktrace->addFrame('path/to/file', 3, ['file' => 'path/to/file', 'line' => 3, 'function' => 'test_function', 'class' => 'TestClass']);
 
         $frames = $stacktrace->getFrames();
 
-        $this->assertCount(2, $frames);
+        $this->assertCount(3, $frames);
         $this->assertEquals($frames, $stacktrace->toArray());
-        $this->assertFrameEquals($frames[0], 'TestClass::test_function', 'path/to/file', 2);
-        $this->assertFrameEquals($frames[1], 'test_function', 'path/to/file', 1);
+        $this->assertFrameEquals($frames[0], 'TestClass::test_function', 'path/to/file', 3);
+        $this->assertFrameEquals($frames[1], 'test_function', 'path/to/file', 2);
+        $this->assertFrameEquals($frames[2], null, 'path/to/file', 1);
     }
 
     public function testStacktraceJsonSerialization(): void
@@ -56,6 +58,7 @@ public function testStacktraceJsonSerialization(): void
 
         $stacktrace->addFrame('path/to/file', 1, ['file' => 'path/to/file', 'line' => 1, 'function' => 'test_function']);
         $stacktrace->addFrame('path/to/file', 2, ['file' => 'path/to/file', 'line' => 2, 'function' => 'test_function', 'class' => 'TestClass']);
+        $stacktrace->addFrame('path/to/file', 3, ['file' => 'path/to/file', 'line' => 3, 'class' => 'TestClass']);
 
         $frames = json_encode($stacktrace->getFrames());
         $serializedStacktrace = json_encode($stacktrace);
@@ -72,6 +75,7 @@ public function testAddFrame(): void
             $this->getJsonFixture('frames/eval.json'),
             $this->getJsonFixture('frames/runtime_created.json'),
             $this->getJsonFixture('frames/function.json'),
+            $this->getJsonFixture('frames/missing_function_key.json'),
         ];
 
         foreach ($frames as $frame) {
@@ -80,10 +84,11 @@ public function testAddFrame(): void
 
         $frames = $stacktrace->getFrames();
 
-        $this->assertCount(3, $frames);
-        $this->assertFrameEquals($frames[0], 'TestClass::test_function', 'path/to/file', 12);
-        $this->assertFrameEquals($frames[1], 'test_function', 'path/to/file', 12);
+        $this->assertCount(4, $frames);
+        $this->assertFrameEquals($frames[0], null, 'path/to/file', 12);
+        $this->assertFrameEquals($frames[1], 'TestClass::test_function', 'path/to/file', 12);
         $this->assertFrameEquals($frames[2], 'test_function', 'path/to/file', 12);
+        $this->assertFrameEquals($frames[3], 'test_function', 'path/to/file', 12);
     }
 
     public function testAddFrameSerializesMethodArguments(): void