diff --git a/src/tools/moc/preprocessor.cpp b/src/tools/moc/preprocessor.cpp
index 51873033c7257b74b5fd071eec10cef1183bc0c1..f253c49995cbffd9746fbef28e444eeeee8b94d7 100644
--- a/src/tools/moc/preprocessor.cpp
+++ b/src/tools/moc/preprocessor.cpp
@@ -661,8 +661,10 @@ Symbols Preprocessor::macroExpandIdentifier(Preprocessor *that, SymbolStack &sym
                     expansion += s;
                 }
             } else if (mode == Hash) {
-                if (index < 0)
+                if (index < 0 || index >= arguments.size()) {
                     that->error("'#' is not followed by a macro parameter");
+                    continue;
+                }
 
                 const Symbols &arg = arguments.at(index);
                 QByteArray stringified;
@@ -681,7 +683,7 @@ Symbols Preprocessor::macroExpandIdentifier(Preprocessor *that, SymbolStack &sym
                     expansion.pop_back();
 
                 Symbol next = s;
-                if (index >= 0) {
+                if (index >= 0 && index < arguments.size()) {
                     const Symbols &arg = arguments.at(index);
                     if (arg.size() == 0) {
                         mode = Normal;
@@ -703,7 +705,7 @@ Symbols Preprocessor::macroExpandIdentifier(Preprocessor *that, SymbolStack &sym
                     expansion += next;
                 }
 
-                if (index >= 0) {
+                if (index >= 0 && index < arguments.size()) {
                     const Symbols &arg = arguments.at(index);
                     for (int i = 1; i < arg.size(); ++i)
                         expansion += arg.at(i);
diff --git a/tests/auto/tools/moc/tst_moc.cpp b/tests/auto/tools/moc/tst_moc.cpp
index 8bef678af9a885843c186ef2bec5e7cc01b78dd5..350c6142d204c9d4702d446cdb60844f9ab51efb 100644
--- a/tests/auto/tools/moc/tst_moc.cpp
+++ b/tests/auto/tools/moc/tst_moc.cpp
@@ -1882,6 +1882,13 @@ void tst_Moc::warnings_data()
         << 1
         << QString()
         << QString("standard input:5: Error: Class declaration lacks Q_OBJECT macro.");
+
+    QTest::newRow("QTBUG-46210: crash on invalid macro")
+        << QByteArray("#define Foo(a, b, c) a b c #a #b #c a##b##c #d\n Foo(45);")
+        << QStringList()
+        << 1
+        << QString("IGNORE_ALL_STDOUT")
+        << QString(":2: Error: '#' is not followed by a macro parameter");
 }
 
 void tst_Moc::warnings()