diff --git a/lib/symbols b/lib/symbols
index 82a6d132d5..31ba7f0eb1 100644
--- a/lib/symbols
+++ b/lib/symbols
@@ -314,7 +314,7 @@ spadesuit          cmsy        127 170 mathord  ♠
 lyxnot             cmsy         54  47 mathrel  /           hiddensymbol
 iffont cmsy
 # kerning is slightly imperfect so that one can see when \not is selected
-\def\not{\lyxnot\mathrel{\kern-11mu}}
+\def\not{\lyxnot}
 else
 \def\not{\kern4mu\lyxnot\kern-19mu}
 endif
@@ -991,11 +991,11 @@ bignplus           stmry 112   0 mathop     x  stmaryrd # caution: named hugenpl
 
 \def\varcopyright{\mathord{c\kern-11mu\varbigcirc}}         stmaryrd
 # kerning is slightly imperfect so that one sees when \[Aa]rrownot is selected
-\def\arrownot{\lyxarrownot\mathrel{\kern-11mu}}             stmaryrd
-\def\Arrownot{\lyxArrownot\mathrel{\kern-10.5mu}}           stmaryrd
+\def\arrownot{\lyxarrownot}                                 stmaryrd
+\def\Arrownot{\lyxArrownot\mathrel{\kern0.5mu}}             stmaryrd
 \def\longarrownot{\mathrel{\kern5.5mu}\arrownot\mathrel{\kern-5.5mu}} stmaryrd
 \def\Longarrownot{\mathrel{\kern5.5mu}\Arrownot\mathrel{\kern-5.5mu}} stmaryrd
-\def\Mapsto{\Mapstochar\mathrel{\kern-2mu}\Rightarrow}   mathrel ⤇ stmaryrd
+\def\Mapsto{\Mapstochar\mathrel\Rightarrow}              mathrel ⤇ stmaryrd
 \def\mapsfrom{\leftarrow\kern-9mu\mapsfromchar}          mathrel ↤ stmaryrd
 \def\Mapsfrom{\Leftarrow\kern-9mu\Mapsfromchar}          mathrel ⤆ stmaryrd
 \def\Longmapsto{\Mapstochar\Longrightarrow}              mathrel ⟾ stmaryrd
@@ -1174,7 +1174,7 @@ iffont cmsy
 \def\Longleftarrow{\Leftarrow\joinrel\Relbar}                   mathrel ⟸
 \def\implies{\Longrightarrow}                                   mathrel ⟹ amsmath
 \def\impliedby{\Longleftarrow}                                  mathrel ⟸ amsmath
-\def\mapsto{\mapstochar\mathrel{\kern-2mu}\rightarrow}          mathrel ↤
+\def\mapsto{\mapstochar\rightarrow}                             mathrel ↤
 \def\longmapsto{\mapstochar\joinrel\relbar\joinrel\rightarrow}  mathrel ⟻
 \def\models{\mathrel{\vert}\joinrel\Relbar}                     mathrel ⊨
 else
diff --git a/src/frontends/qt4/GuiFontMetrics.cpp b/src/frontends/qt4/GuiFontMetrics.cpp
index a0fa6998ab..2f598f43dc 100644
--- a/src/frontends/qt4/GuiFontMetrics.cpp
+++ b/src/frontends/qt4/GuiFontMetrics.cpp
@@ -182,17 +182,28 @@ int GuiFontMetrics::width(docstring const & s) const
 	int * pw = strwidth_cache_[s];
 	if (pw)
 		return *pw;
-	// For some reason QMetrics::width returns a wrong value with Qt5
-	// int w = metrics_.width(toqstr(s));
 	PROFILE_CACHE_MISS(width)
 #endif
-	QTextLayout tl;
-	tl.setText(toqstr(s));
-	tl.setFont(font_);
-	tl.beginLayout();
-	QTextLine line = tl.createLine();
-	tl.endLayout();
-	int w = int(line.naturalTextWidth());
+	/* For some reason QMetrics::width returns a wrong value with Qt5
+	 * with some arabic text. OTOH, QTextLayout is broken for single
+	 * characters with null width (like \not in mathed).
+	*/
+	int w = 0;
+	if (s.length() == 1
+#if QT_VERSION >= 0x040800
+	    || font_.styleName() == "LyX"
+#endif
+	    )
+		w = metrics_.width(toqstr(s));
+	else {
+		QTextLayout tl;
+		tl.setText(toqstr(s));
+		tl.setFont(font_);
+		tl.beginLayout();
+		QTextLine line = tl.createLine();
+		tl.endLayout();
+		w = int(line.naturalTextWidth());
+	}
 #ifdef CACHE_METRICS_WIDTH
 	strwidth_cache_.insert(s, new int(w), s.size() * sizeof(char_type));
 #endif