diff --git a/expander.py b/expander.py
index e4b87f3..a5fa077 100755
--- a/expander.py
+++ b/expander.py
@@ -27,6 +27,30 @@ def is_ignored_line(self, line) -> bool:
             return True
         return False
 
+    def in_block_comment_after(self, line: str, in_comment: bool) -> bool:
+        # returns whether a /* */ comment is still open at the end of line
+        i = 0
+        quote = None  # type: Optional[str]
+        while i < len(line):
+            if in_comment:
+                if line.startswith('*/', i):
+                    in_comment = False
+                    i += 1
+            elif quote:
+                if line[i] == '\\':
+                    i += 1
+                elif line[i] == quote:
+                    quote = None
+            elif line.startswith('//', i):
+                break
+            elif line.startswith('/*', i):
+                in_comment = True
+                i += 1
+            elif line[i] in '"\'':
+                quote = line[i]
+            i += 1
+        return in_comment
+
     def __init__(self, lib_paths: List[Path]):
         self.lib_paths = lib_paths
 
@@ -67,9 +91,11 @@ def expand(self, source: str, origname) -> str:
         self.included = set()
         result = []  # type: List[str]
         linenum = 0
+        in_comment = False
         for line in source.splitlines():
             linenum += 1
-            m = self.atcoder_include.match(line)
+            m = None if in_comment else self.atcoder_include.match(line)
+            in_comment = self.in_block_comment_after(line, in_comment)
             if m:
                 acl_path = self.find_acl(m.group(1))
                 result.extend(self.expand_acl(acl_path))
diff --git a/test/expander/comment_out_multiline.cpp b/test/expander/comment_out_multiline.cpp
new file mode 100644
index 0000000..2b21232
--- /dev/null
+++ b/test/expander/comment_out_multiline.cpp
@@ -0,0 +1,12 @@
+/*
+#include <atcoder/dsu>
+*/
+/* comment */ /*
+#include <atcoder/dsu>
+*/
+const char *s = "/*";
+#include <atcoder/dsu>
+
+int main() {
+    atcoder::dsu uf(10);
+}
diff --git a/test/test_expander.py b/test/test_expander.py
index 28518ea..e278fe7 100755
--- a/test/test_expander.py
+++ b/test/test_expander.py
@@ -42,6 +42,10 @@ def test_comment_out(self):
         self.compile_test(Path('test/expander/comment_out.cpp'),
                           expander_args=['--lib', str(Path.cwd().resolve())])
 
+    def test_comment_out_multiline(self):
+        self.compile_test(Path('test/expander/comment_out_multiline.cpp'),
+                          expander_args=['--lib', str(Path.cwd().resolve())])
+
     def test_env_value(self):
         env = environ.copy()
         env['CPLUS_INCLUDE_PATH'] = str(Path.cwd().resolve())