diff --git a/simplecpp.cpp b/simplecpp.cpp
index 67e59ab..dedd8d6 100755
--- a/simplecpp.cpp
+++ b/simplecpp.cpp
@@ -3445,13 +3445,11 @@ void simplecpp::preprocess(simplecpp::TokenList &output, const simplecpp::TokenL
                     continue;
                 try {
                     const Macro &macro = Macro(rawtok->previous, files);
-                    if (dui.undefined.find(macro.name()) == dui.undefined.end()) {
-                        const MacroMap::iterator it = macros.find(macro.name());
-                        if (it == macros.end())
-                            macros.insert(std::pair<TokenString, Macro>(macro.name(), macro));
-                        else
-                            it->second = macro;
-                    }
+                    const MacroMap::iterator it = macros.find(macro.name());
+                    if (it == macros.end())
+                        macros.insert(std::pair<TokenString, Macro>(macro.name(), macro));
+                    else
+                        it->second = macro;
                 } catch (const std::runtime_error &) {
                     if (outputList) {
                         simplecpp::Output err(files);
diff --git a/test.cpp b/test.cpp
index 8ae2fa2..11f91d7 100644
--- a/test.cpp
+++ b/test.cpp
@@ -2474,6 +2474,18 @@ static void userdef()
     ASSERT_EQUALS("\n123", preprocess(code, dui));
 }
 
+static void userundef_src()
+{
+    const char code[] =
+        "#define A\n"
+        "#ifdef A\n"
+        "123\n"
+        "#endif\n";
+    simplecpp::DUI dui;
+    dui.undefined.insert("A");
+    ASSERT_EQUALS("\n\n123", preprocess(code, dui));
+}
+
 static void utf8()
 {
     ASSERT_EQUALS("123", readfile("\xEF\xBB\xBF 123"));
@@ -3124,6 +3136,7 @@ int main(int argc, char **argv)
     TEST_CASE(undef);
 
     TEST_CASE(userdef);
+    TEST_CASE(userundef_src);
 
     // utf/unicode
     TEST_CASE(utf8);