diff --git a/fortls/regex_patterns.py b/fortls/regex_patterns.py
index 55536976..da808111 100644
--- a/fortls/regex_patterns.py
+++ b/fortls/regex_patterns.py
@@ -133,7 +133,7 @@ class FortranRegularExpressions:
         I,
     )
     PP_DEF_TEST: Pattern = compile(r"(![ ]*)?defined[ ]*\([ ]*(\w*)[ ]*\)$", I)
-    PP_INCLUDE: Pattern = compile(r"[ ]*#[ ]*include[ ]*([\"\w\.]*)", I)
+    PP_INCLUDE: Pattern = compile(r"[ ]*#[ ]*include[ ]*([\"\w\./\\]*)", I)
     PP_ANY: Pattern = compile(r"^[ ]*#:?[ ]*(\w+)")
     # Context matching rules
     CALL: Pattern = compile(r"[ ]*CALL[ ]+[\w%]*$", I)
diff --git a/test/test_regex_patterns.py b/test/test_regex_patterns.py
index f0095660..470fa124 100644
--- a/test/test_regex_patterns.py
+++ b/test/test_regex_patterns.py
@@ -44,3 +44,21 @@ def test_src_file_exts(
     regex = create_src_file_exts_regex(input_exts)
     results = [bool(regex.search(file)) for file in input_files]
     assert results == matches
+
+
+def test_issue_481_include_with_slashes():
+    """Test that preprocessor includes correctly capture directory slashes."""
+    # Import the class instead of the standalone variable
+    from fortls.regex_patterns import FortranRegularExpressions
+
+    # The exact string that was failing for the user
+    test_string = '#include "petsc/finclude/petscvec.h"'
+
+    # Call the regex pattern through the class
+    match = FortranRegularExpressions.PP_INCLUDE.match(test_string)
+
+    # Assert that it found a match
+    assert match is not None
+
+    # Assert that the captured group contains the full path with slashes
+    assert match.group(1) == '"petsc/finclude/petscvec.h"'