diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 59898f5c29b..68b31a7841a 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -496,6 +496,13 @@ QFixed QFontEngine::leading() const
     return m_leading;
 }
 
+
+QFixed QFontEngine::emSquareSize() const
+{
+    qCWarning(lcQpaFonts) << "Font engine does not reimplement emSquareSize(). Returning minimum value.";
+    return 16;
+}
+
 QFixed QFontEngine::ascent() const
 {
     if (!m_heightMetricsQueried)
@@ -2354,6 +2361,9 @@ glyph_metrics_t QFontEngineMulti::boundingBox(glyph_t glyph)
     return engine(which)->boundingBox(stripped(glyph));
 }
 
+QFixed QFontEngineMulti::emSquareSize() const
+{ return engine(0)->emSquareSize(); }
+
 QFixed QFontEngineMulti::ascent() const
 { return engine(0)->ascent(); }
 
diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index 4d1243ccc51..5e2c2963ca4 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/src/gui/text/qfontengine_p.h
@@ -163,7 +163,7 @@ public:
                || QChar::category(ucs4) == QChar::Other_Control;
     }
 
-    virtual QFixed emSquareSize() const { return ascent(); }
+    virtual QFixed emSquareSize() const;
 
     /* returns 0 as glyph index for non existent glyphs */
     virtual glyph_t glyphIndex(uint ucs4) const = 0;
@@ -425,6 +425,7 @@ public:
     virtual glyph_metrics_t boundingBox(glyph_t glyph) override;
     virtual QFontEngine *cloneWithSize(qreal pixelSize) const override;
 
+    virtual QFixed emSquareSize() const override { return _size; }
     virtual QFixed ascent() const override;
     virtual QFixed capHeight() const override;
     virtual QFixed descent() const override;
@@ -463,6 +464,7 @@ public:
     virtual void addOutlineToPath(qreal, qreal, const QGlyphLayout &, QPainterPath *, QTextItem::RenderFlags flags) override;
     virtual void getGlyphBearings(glyph_t glyph, qreal *leftBearing = nullptr, qreal *rightBearing = nullptr) override;
 
+    virtual QFixed emSquareSize() const override;
     virtual QFixed ascent() const override;
     virtual QFixed capHeight() const override;
     virtual QFixed descent() const override;
diff --git a/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp b/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp
index 17b0c431852..3e10cdad44f 100644
--- a/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp
+++ b/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp
@@ -369,6 +369,14 @@ void QWindowsFontEngineDirectWrite::collectMetrics()
     m_directWriteFontFace->GetMetrics(&metrics);
     m_unitsPerEm = metrics.designUnitsPerEm;
 
+    // Something is wrong with this font. Set the em square size to the minimum value in
+    // the spec.
+    if (m_unitsPerEm == 0) {
+        qCWarning(lcQpaFonts) << "Font" << fontDef.families << "reports an em square size of 0."
+                              << "Clamping to minimum value.";
+        m_unitsPerEm = 16;
+    }
+
     m_lineThickness = DESIGN_TO_LOGICAL(metrics.underlineThickness);
     m_capHeight = DESIGN_TO_LOGICAL(metrics.capHeight);
     m_xHeight = DESIGN_TO_LOGICAL(metrics.xHeight);
@@ -497,10 +505,7 @@ bool QWindowsFontEngineDirectWrite::getSfntTableData(uint tag, uchar *buffer, ui
 
 QFixed QWindowsFontEngineDirectWrite::emSquareSize() const
 {
-    if (m_unitsPerEm > 0)
-        return m_unitsPerEm;
-    else
-        return QFontEngine::emSquareSize();
+    return m_unitsPerEm;
 }
 
 glyph_t QWindowsFontEngineDirectWrite::glyphIndex(uint ucs4) const
diff --git a/tests/auto/gui/text/qrawfont/CMakeLists.txt b/tests/auto/gui/text/qrawfont/CMakeLists.txt
index d2a318a2a36..2dcd6615951 100644
--- a/tests/auto/gui/text/qrawfont/CMakeLists.txt
+++ b/tests/auto/gui/text/qrawfont/CMakeLists.txt
@@ -17,6 +17,7 @@ set_source_files_properties("../../../shared/resources/testfont.ttf"
 )
 set(testdata_resource_files
     "../../../shared/resources/testfont.ttf"
+    "testfont_zeroem.ttf"
     "testfont_bold_italic.ttf"
     "testfont_os2_v1.ttf"
 )
diff --git a/tests/auto/gui/text/qrawfont/testfont_zeroem.ttf b/tests/auto/gui/text/qrawfont/testfont_zeroem.ttf
new file mode 100644
index 00000000000..04c469f4966
Binary files /dev/null and b/tests/auto/gui/text/qrawfont/testfont_zeroem.ttf differ
diff --git a/tests/auto/gui/text/qrawfont/tst_qrawfont.cpp b/tests/auto/gui/text/qrawfont/tst_qrawfont.cpp
index 5ec2536718d..252059a7d89 100644
--- a/tests/auto/gui/text/qrawfont/tst_qrawfont.cpp
+++ b/tests/auto/gui/text/qrawfont/tst_qrawfont.cpp
@@ -71,10 +71,13 @@ private slots:
     void qtbug65923_partal_clone_data();
     void qtbug65923_partal_clone();
 
+    void zeroEmSquare();
+
 private:
     QString testFont;
     QString testFontBoldItalic;
     QString testFontOs2V1;
+    QString testFontNoEmSquare;
 #endif // QT_NO_RAWFONT
 };
 
@@ -93,7 +96,9 @@ void tst_QRawFont::initTestCase()
     testFont = QFINDTESTDATA("testfont.ttf");
     testFontBoldItalic = QFINDTESTDATA("testfont_bold_italic.ttf");
     testFontOs2V1 = QFINDTESTDATA("testfont_os2_v1.ttf");
-    if (testFont.isEmpty() || testFontBoldItalic.isEmpty())
+    testFontNoEmSquare = QFINDTESTDATA("testfont_zeroem.ttf");
+
+    if (testFont.isEmpty() || testFontBoldItalic.isEmpty() || testFontNoEmSquare.isEmpty())
         QFAIL("qrawfont unittest font files not found!");
 
     if (QFontDatabase::families().size() == 0)
@@ -1079,6 +1084,12 @@ void tst_QRawFont::qtbug65923_partal_clone()
     QVERIFY(!outerFont.boundingRect(42).isEmpty());
 }
 
+void tst_QRawFont::zeroEmSquare()
+{
+    QRawFont rawFont(testFontNoEmSquare, 12);
+    QVERIFY(!rawFont.isValid() || rawFont.unitsPerEm() > 0);
+}
+
 #endif // QT_NO_RAWFONT
 
 QTEST_MAIN(tst_QRawFont)