diff --git a/selfdrive/modeld/fill_model_msg.py b/selfdrive/modeld/fill_model_msg.py
index 2b8a72b9be..7434e94287 100644
--- a/selfdrive/modeld/fill_model_msg.py
+++ b/selfdrive/modeld/fill_model_msg.py
@@ -92,7 +92,7 @@ def fill_model_msg(msg: capnp._DynamicStructBuilder, net_output_data: Dict[str,
     # interpolate to find `t` for the current xidx
     current_x_val = plan_x[tidx]
     next_x_val = plan_x[tidx+1]
-    p = (ModelConstants.X_IDXS[xidx] - current_x_val) / (next_x_val - current_x_val)
+    p = (ModelConstants.X_IDXS[xidx] - current_x_val) / (next_x_val - current_x_val) if abs(next_x_val - current_x_val) > 1e-9 else float('nan')
     PLAN_T_IDXS[xidx] = p * ModelConstants.T_IDXS[tidx+1] + (1 - p) * ModelConstants.T_IDXS[tidx]
 
   # lane lines