6 files changed, 11 insertions, 0 deletions
diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index d654772e86..6f62d24f1e 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -1410,6 +1410,7 @@ QFontEngineBox::~QFontEngineBox()
 
 bool QFontEngineBox::stringToCMap(const QChar *str, int len, QGlyphLayout *glyphs, int *nglyphs, QFontEngine::ShaperFlags flags) const
 {
+    Q_ASSERT(glyphs->numGlyphs >= *nglyphs);
     if (*nglyphs < len) {
         *nglyphs = len;
         return false;
diff --git a/src/gui/text/qfontengine_ft.cpp b/src/gui/text/qfontengine_ft.cpp
index 43e24b3943..140bf16394 100644
--- a/src/gui/text/qfontengine_ft.cpp
+++ b/src/gui/text/qfontengine_ft.cpp
@@ -1528,6 +1528,7 @@ void QFontEngineFT::addGlyphsToPath(glyph_t *glyphs, QFixedPoint *positions, int
 bool QFontEngineFT::stringToCMap(const QChar *str, int len, QGlyphLayout *glyphs, int *nglyphs,
                                  QFontEngine::ShaperFlags flags) const
 {
+    Q_ASSERT(glyphs->numGlyphs >= *nglyphs);
     if (*nglyphs < len) {
         *nglyphs = len;
         return false;
diff --git a/src/gui/text/qfontengine_qpa.cpp b/src/gui/text/qfontengine_qpa.cpp
index 3ffc809f75..c12cb37edf 100644
--- a/src/gui/text/qfontengine_qpa.cpp
+++ b/src/gui/text/qfontengine_qpa.cpp
@@ -342,6 +342,7 @@ bool QFontEngineQPA::getSfntTableData(uint tag, uchar *buffer, uint *length) con
 
 bool QFontEngineQPA::stringToCMap(const QChar *str, int len, QGlyphLayout *glyphs, int *nglyphs, QFontEngine::ShaperFlags flags) const
 {
+    Q_ASSERT(glyphs->numGlyphs >= *nglyphs);
     if (*nglyphs < len) {
         *nglyphs = len;
         return false;
diff --git a/src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm b/src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm
index 2553cabe2b..4e50d6c53f 100644
--- a/src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm
+++ b/src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm
@@ -195,6 +195,12 @@ void QCoreTextFontEngine::init()
 bool QCoreTextFontEngine::stringToCMap(const QChar *str, int len, QGlyphLayout *glyphs,
                                        int *nglyphs, QFontEngine::ShaperFlags flags) const
 {
+    Q_ASSERT(glyphs->numGlyphs >= *nglyphs);
+    if (*nglyphs < len) {
+        *nglyphs = len;
+        return false;
+    }
+
     QVarLengthArray<CGGlyph> cgGlyphs(len);
     CTFontGetGlyphsForCharacters(ctfont, (const UniChar*)str, cgGlyphs.data(), len);
 
diff --git a/src/plugins/platforms/windows/qwindowsfontengine.cpp b/src/plugins/platforms/windows/qwindowsfontengine.cpp
index 79615e79ec..87eca98e44 100644
--- a/src/plugins/platforms/windows/qwindowsfontengine.cpp
+++ b/src/plugins/platforms/windows/qwindowsfontengine.cpp
@@ -351,6 +351,7 @@ HGDIOBJ QWindowsFontEngine::selectDesignFont() const
 
 bool QWindowsFontEngine::stringToCMap(const QChar *str, int len, QGlyphLayout *glyphs, int *nglyphs, QFontEngine::ShaperFlags flags) const
 {
+    Q_ASSERT(glyphs->numGlyphs >= *nglyphs);
     if (*nglyphs < len) {
         *nglyphs = len;
         return false;
diff --git a/src/plugins/platforms/windows/qwindowsfontenginedirectwrite.cpp b/src/plugins/platforms/windows/qwindowsfontenginedirectwrite.cpp
index 158eee6b38..a4e4dd38d4 100644
--- a/src/plugins/platforms/windows/qwindowsfontenginedirectwrite.cpp
+++ b/src/plugins/platforms/windows/qwindowsfontenginedirectwrite.cpp
@@ -318,6 +318,7 @@ inline unsigned int getChar(const QChar *str, int &i, const int len)
 bool QWindowsFontEngineDirectWrite::stringToCMap(const QChar *str, int len, QGlyphLayout *glyphs,
                                                  int *nglyphs, QFontEngine::ShaperFlags flags) const
 {
+    Q_ASSERT(glyphs->numGlyphs >= *nglyphs);
     if (*nglyphs < len) {
         *nglyphs = len;
         return false;