diff --git a/simplecpp.cpp b/simplecpp.cpp
index 7774fd29..67ea3490 100644
--- a/simplecpp.cpp
+++ b/simplecpp.cpp
@@ -2450,7 +2450,7 @@ namespace simplecpp {
 
     bool isAbsolutePath(const std::string &path)
     {
-#ifdef SIMPLECPP_WINDOWS
+#if defined(_WIN32) || defined(__CYGWIN__) || defined(__MINGW32__) || defined(__MSYS__)
         // C:\\path\\file
         // C:/path/file
         if (path.length() >= 3 && std::isalpha(path[0]) && path[1] == ':' && (path[2] == '\\' || path[2] == '/'))
@@ -2460,10 +2460,12 @@ namespace simplecpp {
         // //host/path/file
         if (path.length() >= 2 && (path[0] == '\\' || path[0] == '/') && (path[1] == '\\' || path[1] == '/'))
             return true;
+#endif
 
-        return false;
-#else
+#if !defined(_WIN32) || defined(__MINGW32__)
         return !path.empty() && path[0] == '/';
+#else
+        return false;
 #endif
     }
 }
diff --git a/test.cpp b/test.cpp
index 26e3b95b..3922cb38 100644
--- a/test.cpp
+++ b/test.cpp
@@ -3257,36 +3257,44 @@ static void safe_api()
 }
 
 static void isAbsolutePath() {
-#ifdef _WIN32
-    ASSERT_EQUALS(true, simplecpp::isAbsolutePath("C:\\foo\\bar"));
-    ASSERT_EQUALS(true, simplecpp::isAbsolutePath("C:/foo/bar"));
-    ASSERT_EQUALS(true, simplecpp::isAbsolutePath("\\\\foo\\bar"));
+#if defined(_WIN32) || defined(__CYGWIN__) || defined(__MINGW32__) || defined(__MSYS__)
+    constexpr bool supportsWin = true;
+#else
+    constexpr bool supportsWin = false;
+#endif
+
+#if !defined(_WIN32) || defined(__MINGW32__)
+    constexpr bool supportsUnx = true;
+#else
+    constexpr bool supportsUnx = false;
+#endif
+
+    // valid Windows paths
+    ASSERT_EQUALS(supportsWin, simplecpp::isAbsolutePath("C:\\foo\\bar"));
+    ASSERT_EQUALS(supportsWin, simplecpp::isAbsolutePath("C:/foo/bar"));
+    ASSERT_EQUALS(supportsWin, simplecpp::isAbsolutePath("\\\\foo\\bar"));
+
+    // valid Unix paths
+    ASSERT_EQUALS(supportsUnx, simplecpp::isAbsolutePath("/foo/bar"));
+    ASSERT_EQUALS(supportsUnx, simplecpp::isAbsolutePath("/"));
+
+    // valid Windows and Unix paths
+    ASSERT_EQUALS(supportsWin || supportsUnx, simplecpp::isAbsolutePath("//host/foo/bar"));
 
+    // invalid paths
     ASSERT_EQUALS(false, simplecpp::isAbsolutePath("foo\\bar"));
     ASSERT_EQUALS(false, simplecpp::isAbsolutePath("foo/bar"));
     ASSERT_EQUALS(false, simplecpp::isAbsolutePath("foo.cpp"));
     ASSERT_EQUALS(false, simplecpp::isAbsolutePath("C:foo.cpp"));
     ASSERT_EQUALS(false, simplecpp::isAbsolutePath("C:foo\\bar.cpp"));
     ASSERT_EQUALS(false, simplecpp::isAbsolutePath("bar.cpp"));
-    //ASSERT_EQUALS(true, simplecpp::isAbsolutePath("\\")); // TODO
     ASSERT_EQUALS(false, simplecpp::isAbsolutePath("0:\\foo\\bar"));
     ASSERT_EQUALS(false, simplecpp::isAbsolutePath("0:/foo/bar"));
     ASSERT_EQUALS(false, simplecpp::isAbsolutePath("\\foo\\bar"));
+
+    //ASSERT_EQUALS(true, simplecpp::isAbsolutePath("\\")); // TODO
     //ASSERT_EQUALS(false, simplecpp::isAbsolutePath("\\\\")); // TODO
     //ASSERT_EQUALS(false, simplecpp::isAbsolutePath("//")); // TODO
-    ASSERT_EQUALS(false, simplecpp::isAbsolutePath("/foo/bar"));
-    ASSERT_EQUALS(false, simplecpp::isAbsolutePath("/"));
-#else
-    ASSERT_EQUALS(true, simplecpp::isAbsolutePath("/foo/bar"));
-    ASSERT_EQUALS(true, simplecpp::isAbsolutePath("/"));
-    ASSERT_EQUALS(true, simplecpp::isAbsolutePath("//host/foo/bar"));
-
-    ASSERT_EQUALS(false, simplecpp::isAbsolutePath("foo/bar"));
-    ASSERT_EQUALS(false, simplecpp::isAbsolutePath("foo.cpp"));
-    ASSERT_EQUALS(false, simplecpp::isAbsolutePath("C:\\foo\\bar"));
-    ASSERT_EQUALS(false, simplecpp::isAbsolutePath("C:/foo/bar"));
-    ASSERT_EQUALS(false, simplecpp::isAbsolutePath("\\\\foo\\bar"));
-#endif
 }
 
 // crashes detected by fuzzer