diff --git a/src/errors/mod.rs b/src/errors/mod.rs
index 5a22934..f4556e9 100644
--- a/src/errors/mod.rs
+++ b/src/errors/mod.rs
@@ -158,6 +158,9 @@ pub enum BSVErrors {
     #[error("Error deserialising TxOut field {0}: {1}")]
     DeserialiseTxOut(String, #[source] std::io::Error),
 
+    #[error("NonScriptData can only appear after an OP_RETURN that is not in a branch block!")]
+    InvalidNonScriptData(),
+
     #[error("Error serialising TxOut field {0}: {1}")]
     SerialiseTxOut(String, #[source] std::io::Error),
 
diff --git a/src/script/mod.rs b/src/script/mod.rs
index bd437ef..154d4db 100644
--- a/src/script/mod.rs
+++ b/src/script/mod.rs
@@ -240,13 +240,6 @@ impl Script {
     fn map_string_to_script_bit(code: &str, is_non_script_data: bool) -> Result<ScriptBit, BSVErrors> {
         let code = code.trim();
 
-        if is_non_script_data {
-            if code.starts_with("non-script-data:") {
-                let non_script_data = hex::decode(code.trim_start_matches("non-script-data:"))?;
-                return Ok(ScriptBit::NonScriptData(non_script_data));
-            }
-        }
-
         // Number OP_CODES
         match code {
             "0" => return Ok(ScriptBit::OpCode(OpCodes::OP_0)),
@@ -274,6 +267,15 @@ impl Script {
             return Ok(ScriptBit::OpCode(opcode));
         }
 
+        if code.starts_with("non-script-data:") {
+            if is_non_script_data {
+                let non_script_data = hex::decode(code.trim_start_matches("non-script-data:"))?;
+                return Ok(ScriptBit::NonScriptData(non_script_data));
+            } else {
+                return Err(BSVErrors::InvalidNonScriptData());
+            }
+        }
+
         // PUSHDATA OP_CODES
         let data_bytes = hex::decode(code)?;
         let bit = match VarInt::get_pushdata_opcode(data_bytes.len() as u64) {
@@ -340,7 +342,7 @@ impl Script {
     }
 
     /**
-     * Ordinary ASM, (for example, OP_RETURN 01 01) does not contain ScriptBit::NonScriptData after being converted into ScriptBit. 
+     * Ordinary ASM, (for example, OP_RETURN 01 01) does not contain ScriptBit::NonScriptData after being converted into ScriptBit.
      * This function wraps all ScriptBit after OP_RETURN with ScriptBit::NonScriptData.
      */
     fn wrap_with_non_script_data(bits_iter: &mut Iter<ScriptBit>, non_script_data_index: usize) -> Vec<ScriptBit> {
diff --git a/tests/script.rs b/tests/script.rs
index 07d1be1..ab11c3a 100644
--- a/tests/script.rs
+++ b/tests/script.rs
@@ -1,6 +1,6 @@
 #[cfg(test)]
 mod script_tests {
-    use bsv::{Hash, OpCodes, P2PKHAddress, Script, ScriptBit};
+    use bsv::{BSVErrors, Hash, OpCodes, P2PKHAddress, Script, ScriptBit};
     // #[test]
     // #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
     // fn to_hex_string() {
@@ -540,7 +540,6 @@ mod script_tests {
         assert_eq!(&script.to_hex(), "006a0051");
     }
 
-
     #[test]
     fn non_script_data_asm() {
         let script = Script::from_asm_string("0 OP_RETURN 01 0102").unwrap();
@@ -554,4 +553,14 @@ mod script_tests {
         assert_eq!(&script.to_hex(), "006a0101020102");
     }
 
+    #[test]
+    fn invalid_non_script_data() {
+        let result = Script::from_asm_string("0 non-script-data:0101020102 01 0102 OP_RETURN");
+
+        assert!(matches!(result, Err(BSVErrors::InvalidNonScriptData())));
+
+        let result = Script::from_asm_string("OP_1 OP_IF OP_1 OP_RETURN non-script-data:0101020102 01 0102 OP_ENDIF OP_1");
+
+        assert!(matches!(result, Err(BSVErrors::InvalidNonScriptData())));
+    }
 }