diff --git a/dpgen/data/gen.py b/dpgen/data/gen.py
index 27134ef64..003e7fda8 100644
--- a/dpgen/data/gen.py
+++ b/dpgen/data/gen.py
@@ -237,12 +237,24 @@ def poscar_scale_cartesian(str_in, scale):
 def poscar_scale(poscar_in, poscar_out, scale):
     with open(poscar_in) as fin:
         lines = list(fin)
-    if "D" == lines[7][0] or "d" == lines[7][0]:
+
+    # Determine if "Selective dynamics" is present
+    if lines[7].strip().lower().startswith("s"):
+        coord_type_line = 8  # If present, coordinates type is on line 9
+    else:
+        coord_type_line = 7  # If not, coordinates type is on line 8
+
+    # Process according to the coordinate type
+    if "D" == lines[coord_type_line][0] or "d" == lines[coord_type_line][0]:
         lines = poscar_scale_direct(lines, scale)
-    elif "C" == lines[7][0] or "c" == lines[7][0]:
+    elif "C" == lines[coord_type_line][0] or "c" == lines[coord_type_line][0]:
         lines = poscar_scale_cartesian(lines, scale)
     else:
-        raise RuntimeError("Unknow poscar style at line 7: %s" % lines[7])
+        raise RuntimeError(
+            f"Unknown poscar style at line {coord_type_line + 1}: {lines[coord_type_line]}"
+        )
+
+    # Write scaled positions back to output file
     with open(poscar_out, "w") as fout:
         fout.write("".join(lines))