diff --git a/sim/src/tlv.rs b/sim/src/tlv.rs
index ad53c27..fa2fa7e 100644
--- a/sim/src/tlv.rs
+++ b/sim/src/tlv.rs
@@ -98,8 +98,6 @@
 pub struct TlvGen {
     flags: u32,
     kinds: Vec<TlvKinds>,
-    /// The total size of the payload.
-    size: u16,
     payload: Vec<u8>,
     dependencies: Vec<Dependency>,
     enc_key: Vec<u8>,
@@ -121,7 +119,6 @@
     pub fn new_hash_only() -> TlvGen {
         TlvGen {
             kinds: vec![TlvKinds::SHA256],
-            size: 4 + 32,
             ..Default::default()
         }
     }
@@ -130,7 +127,6 @@
     pub fn new_rsa_pss() -> TlvGen {
         TlvGen {
             kinds: vec![TlvKinds::SHA256, TlvKinds::RSA2048],
-            size: 4 + 32 + 4 + 32 + 4 + 256,
             ..Default::default()
         }
     }
@@ -139,7 +135,6 @@
     pub fn new_rsa3072_pss() -> TlvGen {
         TlvGen {
             kinds: vec![TlvKinds::SHA256, TlvKinds::RSA3072],
-            size: 4 + 32 + 4 + 32 + 4 + 384,
             ..Default::default()
         }
     }
@@ -148,7 +143,6 @@
     pub fn new_ecdsa() -> TlvGen {
         TlvGen {
             kinds: vec![TlvKinds::SHA256, TlvKinds::ECDSA256],
-            size: 4 + 32 + 4 + 32 + 4 + 72,
             ..Default::default()
         }
     }
@@ -157,7 +151,6 @@
     pub fn new_ed25519() -> TlvGen {
         TlvGen {
             kinds: vec![TlvKinds::SHA256, TlvKinds::ED25519],
-            size: 4 + 32 + 4 + 32 + 4 + 64,
             ..Default::default()
         }
     }
@@ -167,7 +160,6 @@
         TlvGen {
             flags: TlvFlags::ENCRYPTED as u32,
             kinds: vec![TlvKinds::SHA256, TlvKinds::ENCRSA2048],
-            size: 4 + 32 + 4 + 256,
             ..Default::default()
         }
     }
@@ -177,7 +169,6 @@
         TlvGen {
             flags: TlvFlags::ENCRYPTED as u32,
             kinds: vec![TlvKinds::SHA256, TlvKinds::RSA2048, TlvKinds::ENCRSA2048],
-            size: 4 + 32 + 4 + 32 + 4 + 256 + 4 + 256,
             ..Default::default()
         }
     }
@@ -187,7 +178,6 @@
         TlvGen {
             flags: TlvFlags::ENCRYPTED as u32,
             kinds: vec![TlvKinds::SHA256, TlvKinds::ENCKW128],
-            size: 4 + 32 + 4 + 24,
             ..Default::default()
         }
     }
@@ -197,7 +187,6 @@
         TlvGen {
             flags: TlvFlags::ENCRYPTED as u32,
             kinds: vec![TlvKinds::SHA256, TlvKinds::RSA2048, TlvKinds::ENCKW128],
-            size: 4 + 32 + 4 + 32 + 4 + 256 + 4 + 24,
             ..Default::default()
         }
     }
@@ -207,7 +196,6 @@
         TlvGen {
             flags: TlvFlags::ENCRYPTED as u32,
             kinds: vec![TlvKinds::SHA256, TlvKinds::ECDSA256, TlvKinds::ENCKW128],
-            size: 4 + 32 + 4 + 32 + 4 + 72 + 4 + 24,
             ..Default::default()
         }
     }
@@ -217,7 +205,6 @@
         TlvGen {
             flags: TlvFlags::ENCRYPTED as u32,
             kinds: vec![TlvKinds::SHA256, TlvKinds::ENCEC256],
-            size: 4 + 32 + 4 + 32 + 4 + 113,
             ..Default::default()
         }
     }
@@ -227,15 +214,9 @@
         TlvGen {
             flags: TlvFlags::ENCRYPTED as u32,
             kinds: vec![TlvKinds::SHA256, TlvKinds::ECDSA256, TlvKinds::ENCEC256],
-            size: 4 + 32 + 4 + 32 + 4 + 72 + 4 + 113,
             ..Default::default()
         }
     }
-
-    /// Retrieve the size that the TLV will occupy.  This can be called at any time.
-    pub fn get_size(&self) -> u16 {
-        4 + self.size
-    }
 }
 
 impl ManifestGen for TlvGen {
@@ -263,8 +244,6 @@
     }
 
     fn add_dependency(&mut self, id: u8, version: &ImageVersion) {
-        let my_size = 4 + 4 + 8;
-        self.size += my_size;
         self.dependencies.push(Dependency {
             id: id,
             version: version.clone(),
@@ -318,9 +297,11 @@
         result.extend_from_slice(&protected_tlv);
 
         // add non-protected payload
+        let npro_pos = result.len();
         result.push(0x07);
         result.push(0x69);
-        result.write_u16::<LittleEndian>(self.get_size()).unwrap();
+        // Placeholder for the size.
+        result.write_u16::<LittleEndian>(0).unwrap();
 
         if self.kinds.contains(&TlvKinds::SHA256) {
             // If a signature is not requested, corrupt the hash we are
@@ -564,6 +545,11 @@
             result.extend_from_slice(&buf);
         }
 
+        // Patch the size back into the TLV header.
+        let size = (result.len() - npro_pos) as u16;
+        let mut size_buf = &mut result[npro_pos + 2 .. npro_pos + 4];
+        size_buf.write_u16::<LittleEndian>(size).unwrap();
+
         result
     }