diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8a478156..1b78a65e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,6 +26,9 @@
   ([#219](https://github.com/fortran-lang/fortls/issues/219))
 - Changed hover messages and signature help to use Markdown
   ([#45](https://github.com/fortran-lang/fortls/issues/45))
+- Changed automatic detection of fixed/free-form of files to ignore
+  preprocessor lines.
+  ([#302](https://github.com/fortran-lang/fortls/pull/302))
 
 ### Fixed
 
diff --git a/fortls/helper_functions.py b/fortls/helper_functions.py
index b5e42167..fd1a9030 100644
--- a/fortls/helper_functions.py
+++ b/fortls/helper_functions.py
@@ -68,8 +68,31 @@ def detect_fixed_format(file_lines: list[str]) -> bool:
     Lines wih ampersands are not fixed format
     >>> detect_fixed_format(['trailing line & ! comment'])
     False
+
+    But preprocessor lines will be ignored
+    >>> detect_fixed_format(
+    ...     ['#if defined(A) && !defined(B)', 'C Fixed format', '#endif'])
+    True
+
+    >>> detect_fixed_format(
+    ...     ['#if defined(A) && !defined(B)', ' free format', '#endif'])
+    False
+
+    And preprocessor line-continuation is taken into account
+    >>> detect_fixed_format(
+    ...     ['#if defined(A) \\\\ ', ' && !defined(B)', 'C Fixed format', '#endif'])
+    True
+
+    >>> detect_fixed_format(
+    ...     ['#if defined(A) \\\\', '&& \\\\', '!defined(B)', ' free format', '#endif'])
+    False
     """
+    pp_continue = False
     for line in file_lines:
+        # Ignore preprocessor lines
+        if line.startswith("#") or pp_continue:
+            pp_continue = line.rstrip().endswith("\\")
+            continue
         if FRegex.FREE_FORMAT_TEST.match(line):
             return False
         tmp_match = FRegex.VAR.match(line)