diff --git a/src/bin/ponderosa-asm.rs b/src/bin/ponderosa-asm.rs
index 8ae5866..b97d4f8 100644
--- a/src/bin/ponderosa-asm.rs
+++ b/src/bin/ponderosa-asm.rs
@@ -88,7 +88,12 @@ fn parse_forestry_op(tokens: &Vec<&str>, opcode: u16) -> Result<u16, String> {
     } else if relative_y > 15 || relative_y < -16 {
         Err(format!("Cannot reach cell at {relative_y} along the Y-axis; trees may only access cells in the range of -16 to 15"))
     } else {
-        Ok(opcode<<11 | stack<<10 | (relative_x as u16)<<5 | (relative_y as u16))
+        Ok(
+            opcode<<11
+            | stack<<10
+            | ((relative_x as u16)<<5) & 0b11111
+            | (relative_y as u16) & 0b11111
+        )
     }
 }