diff --git a/tests/test_safe_output_path.py b/tests/test_safe_output_path.py
index 1c559b0..8f49a32 100644
--- a/tests/test_safe_output_path.py
+++ b/tests/test_safe_output_path.py
@@ -54,6 +54,27 @@ def test_wrong_extension_is_replaced(self):
             tools._safe_output_path("plan.exe", ".pdf"), self.save_dir / "plan.pdf"
         )
 
+    def test_longer_real_extension_is_replaced(self):
+        self.assertEqual(
+            tools._safe_output_path("plan.jpeg", ".pdf"), self.save_dir / "plan.pdf"
+        )
+
+    def test_dotted_sheet_name_keeps_its_tail(self):
+        # The tail is not an extension, so it stays in the name.
+        self.assertEqual(
+            tools._safe_output_path("Sheet A.1", ".dwg"),
+            self.save_dir / "Sheet A.1.dwg",
+        )
+        self.assertEqual(
+            tools._safe_output_path("Sheet 1.A", ".dwg"),
+            self.save_dir / "Sheet 1.A.dwg",
+        )
+
+    def test_dotted_sheet_names_do_not_share_a_file(self):
+        first = tools._safe_output_path("Sheet A.1", ".dwg")
+        second = tools._safe_output_path("Sheet A.2", ".dwg")
+        self.assertNotEqual(first, second)
+
     def test_subfolder_is_allowed_and_created(self):
         target = tools._safe_output_path("floor-1/plan.dwg", ".dwg")
         self.assertEqual(target, self.save_dir / "floor-1" / "plan.dwg")
diff --git a/tools.py b/tools.py
index 037d572..409b90f 100644
--- a/tools.py
+++ b/tools.py
@@ -59,6 +59,12 @@ def _color_index(color: str | int | None) -> int | None:
     )
 
 
+# A dot is read as a file extension only when two to four ASCII letters follow
+# it (.dwg, .pdf, .exe, .jpeg). Any other tail, such as "Sheet A.1" or
+# "Sheet 1.A", is part of the name and is kept.
+_EXTENSION_SHAPE = re.compile(r"\.[A-Za-z]{2,4}")
+
+
 def _safe_output_path(filename: str, extension: str) -> Path:
     """Resolve filename inside the one folder the server may write to."""
     candidate = Path(str(filename).strip().strip('"').strip("'"))
@@ -69,7 +75,10 @@ def _safe_output_path(filename: str, extension: str) -> Path:
     if not candidate.name:
         raise AcadError("A file name is required.")
     if candidate.suffix.lower() != extension:
-        candidate = candidate.with_suffix(extension)
+        if _EXTENSION_SHAPE.fullmatch(candidate.suffix):
+            candidate = candidate.with_suffix(extension)
+        else:
+            candidate = candidate.with_name(candidate.name + extension)
 
     resolved = (config.SAVE_DIR / candidate).resolve()
     # A path comparison, not a string prefix: "...\Out-other" starts with