diff --git a/CHANGES b/CHANGES
index 0ae8cb26d..c8e0bb941 100644
--- a/CHANGES
+++ b/CHANGES
@@ -13,6 +13,7 @@ Bugs fixed
 * #3150: Fix query word splitter in JavaScript. It behaves as same as Python's regular expression.
 * #3093: gettext build broken on substituted images.
 * #3093: gettext build broken on image node under ``note`` directive.
+* imgmath: crashes on showing error messages if image generation failed
 
 Release 1.4.8 (released Oct 1, 2016)
 ====================================
diff --git a/sphinx/ext/imgmath.py b/sphinx/ext/imgmath.py
index f8e402be3..9b75800af 100644
--- a/sphinx/ext/imgmath.py
+++ b/sphinx/ext/imgmath.py
@@ -245,10 +245,11 @@ def html_visit_displaymath(self, node):
     try:
         fname, depth = render_math(self, latex)
     except MathExtError as exc:
-        sm = nodes.system_message(str(exc), type='WARNING', level=2,
+        msg = text_type(exc)
+        sm = nodes.system_message(msg, type='WARNING', level=2,
                                   backrefs=[], source=node['latex'])
         sm.walkabout(self)
-        self.builder.warn('inline latex %r: ' % node['latex'] + str(exc))
+        self.builder.warn('inline latex %r: ' % node['latex'] + msg)
         raise nodes.SkipNode
     self.body.append(self.starttag(node, 'div', CLASS='math'))
     self.body.append('<p>')
diff --git a/sphinx/ext/pngmath.py b/sphinx/ext/pngmath.py
index d7660550e..655eb562f 100644
--- a/sphinx/ext/pngmath.py
+++ b/sphinx/ext/pngmath.py
@@ -218,10 +218,11 @@ def html_visit_displaymath(self, node):
     try:
         fname, depth = render_math(self, latex)
     except MathExtError as exc:
-        sm = nodes.system_message(str(exc), type='WARNING', level=2,
+        msg = text_type(exc)
+        sm = nodes.system_message(msg, type='WARNING', level=2,
                                   backrefs=[], source=node['latex'])
         sm.walkabout(self)
-        self.builder.warn('inline latex %r: ' % node['latex'] + str(exc))
+        self.builder.warn('inline latex %r: ' % node['latex'] + msg)
         raise nodes.SkipNode
     self.body.append(self.starttag(node, 'div', CLASS='math'))
     self.body.append('<p>')