diff --git a/simplecpp.cpp b/simplecpp.cpp
index 599ffdfe..68db40f3 100755
--- a/simplecpp.cpp
+++ b/simplecpp.cpp
@@ -2681,13 +2681,16 @@ static void simplifySizeof(simplecpp::TokenList &expr, const std::map<std::strin
     }
 }
 
-/** Evaluate __has_include(file) */
 static bool isCpp17OrLater(const simplecpp::DUI &dui)
 {
     const std::string std_ver = simplecpp::getCppStdString(dui.std);
     return !std_ver.empty() && (std_ver >= "201703L");
 }
 
+static bool isGnu(const simplecpp::DUI &dui)
+{
+    return dui.std.rfind("gnu", 0) != std::string::npos;
+}
 
 static std::string currentDirectoryOSCalc() {
     const std::size_t size = 4096;
@@ -2760,7 +2763,7 @@ static std::string extractRelativePathFromAbsolute(const std::string& absoluteSi
 static std::string openHeader(std::ifstream &f, const simplecpp::DUI &dui, const std::string &sourcefile, const std::string &header, bool systemheader);
 static void simplifyHasInclude(simplecpp::TokenList &expr, const simplecpp::DUI &dui)
 {
-    if (!isCpp17OrLater(dui))
+    if (!isCpp17OrLater(dui) && !isGnu(dui))
         return;
 
     for (simplecpp::Token *tok = expr.front(); tok; tok = tok->next) {
@@ -3483,7 +3486,7 @@ void simplecpp::preprocess(simplecpp::TokenList &output, const simplecpp::TokenL
     // use a dummy vector for the macros because as this is not part of the file and would add an empty entry - e.g. /usr/include/poll.h
     std::vector<std::string> dummy;
 
-    const bool hasInclude = isCpp17OrLater(dui);
+    const bool hasInclude = isCpp17OrLater(dui) || isGnu(dui);
     MacroMap macros;
     for (std::list<std::string>::const_iterator it = dui.defines.begin(); it != dui.defines.end(); ++it) {
         const std::string &macrostr = *it;
diff --git a/test.cpp b/test.cpp
index cec253b8..edd52f92 100644
--- a/test.cpp
+++ b/test.cpp
@@ -1563,6 +1563,21 @@ static void has_include_5()
     ASSERT_EQUALS("", preprocess(code));
 }
 
+static void has_include_6()
+{
+    const char code[] = "#if defined( __has_include)\n"
+                        "  #if !__has_include(<testsuite/unrealFileName2.abcdef>)\n"
+                        "    A\n"
+                        "  #else\n"
+                        "    B\n"
+                        "  #endif\n"
+                        "#endif";
+    simplecpp::DUI dui;
+    dui.std = "gnu99";
+    ASSERT_EQUALS("\n\nA", preprocess(code, dui));
+    ASSERT_EQUALS("", preprocess(code));
+}
+
 static void ifdef1()
 {
     const char code[] = "#ifdef A\n"
@@ -3123,6 +3138,7 @@ int main(int argc, char **argv)
     TEST_CASE(has_include_3);
     TEST_CASE(has_include_4);
     TEST_CASE(has_include_5);
+    TEST_CASE(has_include_6);
 
     TEST_CASE(ifdef1);
     TEST_CASE(ifdef2);