diff --git a/src/main/java/stirling/software/SPDF/model/api/security/SignPDFWithCertRequest.java b/src/main/java/stirling/software/SPDF/model/api/security/SignPDFWithCertRequest.java
index b332031c0..e6d20a7ef 100644
--- a/src/main/java/stirling/software/SPDF/model/api/security/SignPDFWithCertRequest.java
+++ b/src/main/java/stirling/software/SPDF/model/api/security/SignPDFWithCertRequest.java
@@ -15,7 +15,8 @@ public class SignPDFWithCertRequest extends PDFFile {
 
     @Schema(
             description = "The type of the digital certificate",
-            allowableValues = {"PEM", "PKCS12", "JKS"})
+            allowableValues = {"PEM", "PKCS12", "JKS"},
+            requiredMode = Schema.RequiredMode.REQUIRED)
     private String certType;
 
     @Schema(