diff --git a/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDDocument.java b/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDDocument.java
index 2d681467de7..f78c5b3cb52 100644
--- a/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDDocument.java
+++ b/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDDocument.java
@@ -367,10 +367,9 @@ public void addSignature(PDSignature sigObject, SignatureInterface signatureInte
         }
 
         PDSignatureField signatureField = null;
-        COSBase cosFieldBase = acroForm.getCOSObject().getDictionaryObject(COSName.FIELDS);
-        if (cosFieldBase instanceof COSArray)
+        COSArray fieldArray = acroForm.getCOSObject().getCOSArray(COSName.FIELDS);
+        if (fieldArray != null)
         {
-            COSArray fieldArray = (COSArray) cosFieldBase;
             fieldArray.setNeedToBeUpdated(true);
             signatureField = findSignatureField(acroForm.getFieldIterator(), sigObject);
         }