diff --git a/src/packet/BOOTP.py b/src/packet/BOOTP.py
index 173e5e0f3ce66052fba04862585806c54340b500..a095de0672ed09ca42591f631f40313e0d3bc445 100644
--- a/src/packet/BOOTP.py
+++ b/src/packet/BOOTP.py
@@ -70,6 +70,10 @@ class BOOTP(Packet):
         # Get field which will be modified
         field = random.choice(self.fields)
 
+        # Initialize old and new values
+        old_value = None
+        new_value = None
+
         if field == "chaddr":
             old_value = self.layer.getfieldval("chaddr")  # Store old value of field
             new_value = Packet.bytes_edit_char(old_value[:6]) + old_value[6:]  # Randomly change one byte in the MAC address
diff --git a/src/packet/CoAP.py b/src/packet/CoAP.py
index 7f940f18d400f5c39de24f35811a5f2f125dcf53..9d79806abd578c06d9c999a900734f3e768928ab 100644
--- a/src/packet/CoAP.py
+++ b/src/packet/CoAP.py
@@ -80,6 +80,10 @@ class CoAP(Packet):
         # Get field which will be modified
         field = random.choice(self.fields)
 
+        # Initialize old and new values
+        old_value = None
+        new_value = None
+
         # Chosen field is an integer
         if field == "type" or field == "code":
             old_value = self.layer.getfieldval(field)
diff --git a/src/packet/DNS.py b/src/packet/DNS.py
index b5ad2fae7b2ca05b666ef7ec8a456ff52ac1b2da..ce8fb303f111c18a04caeb9c4abb6c462e696e73 100644
--- a/src/packet/DNS.py
+++ b/src/packet/DNS.py
@@ -52,6 +52,10 @@ class DNS(Packet):
         # Get auxiliary fields
         qdcount = self.layer.getfieldval("qdcount")
         question_record = self.layer.getfieldval("qd") if qdcount > 0 else None
+
+        # Initialize old and new values
+        old_value = None
+        new_value = None
         
         # Field is QR flag
         if field == "qr":