diff --git a/src/corelib/tools/qstringbuilder.cpp b/src/corelib/tools/qstringbuilder.cpp
index 45de6bc1c3..1cc7e5d2c3 100644
--- a/src/corelib/tools/qstringbuilder.cpp
+++ b/src/corelib/tools/qstringbuilder.cpp
@@ -162,6 +162,8 @@ void QAbstractConcatenable::convertFromAscii(const char *a, int len, QChar *&out
     }
 #endif
     if (len == -1) {
+        if (!a)
+            return;
         while (*a)
             *out++ = QLatin1Char(*a++);
     } else {
diff --git a/src/corelib/tools/qstringbuilder.h b/src/corelib/tools/qstringbuilder.h
index 709d84a578..594ab2f183 100644
--- a/src/corelib/tools/qstringbuilder.h
+++ b/src/corelib/tools/qstringbuilder.h
@@ -352,6 +352,8 @@ template <> struct QConcatenable<const char *> : private QAbstractConcatenable
 #endif
     static inline void appendTo(const char *a, char *&out)
     {
+        if (!a)
+            return;
         while (*a)
             *out++ = *a++;
     }
diff --git a/tests/auto/qstringbuilder1/stringbuilder.cpp b/tests/auto/qstringbuilder1/stringbuilder.cpp
index 2327ef55f9..de7ad656e4 100644
--- a/tests/auto/qstringbuilder1/stringbuilder.cpp
+++ b/tests/auto/qstringbuilder1/stringbuilder.cpp
@@ -133,6 +133,12 @@ void runScenario()
     QCOMPARE(r, string);
     r = string P ba;
     QCOMPARE(r, string);
+
+    const char *zero = 0;
+    r = string P zero;
+    QCOMPARE(r, string);
+    r = zero P string;
+    QCOMPARE(r, string);
 #endif
 
     string = QString::fromLatin1(LITERAL);
@@ -161,6 +167,12 @@ void runScenario()
         QCOMPARE(r, r2);
         r2 = QByteArray("hello\0") P UTF8_LITERAL;
         QCOMPARE(r, r2);
+
+        const char *zero = 0;
+        r = ba P zero;
+        QCOMPARE(r, ba);
+        r = zero P ba;
+        QCOMPARE(r, ba);
     }
 
     //operator QString  +=