diff --git a/pkgs/applications/kde-apps-15.04/cantor/0001-qalculate-filename-string-type.patch b/pkgs/applications/kde-apps-15.04/cantor/0001-qalculate-filename-string-type.patch
new file mode 100644
index 00000000000..b2679b95a86
--- /dev/null
+++ b/pkgs/applications/kde-apps-15.04/cantor/0001-qalculate-filename-string-type.patch
@@ -0,0 +1,28 @@
+From 1a526e40ffc1d6cb050334e8641d8b90d9858a54 Mon Sep 17 00:00:00 2001
+From: Thomas Tuegel <ttuegel@gmail.com>
+Date: Sun, 30 Aug 2015 07:05:03 -0500
+Subject: [PATCH] qalculate filename string type
+
+---
+ src/backends/qalculate/qalculateexpression.cpp | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/src/backends/qalculate/qalculateexpression.cpp b/src/backends/qalculate/qalculateexpression.cpp
+index 1891baa..b2a1984 100644
+--- a/src/backends/qalculate/qalculateexpression.cpp
++++ b/src/backends/qalculate/qalculateexpression.cpp
+@@ -771,9 +771,9 @@ void QalculateExpression::evaluatePlotCommand()
+ 	if (plotParameters.filetype == PLOT_FILETYPE_EPS ||
+ 	    plotParameters.filetype == PLOT_FILETYPE_PS  ||
+ 	    (plotParameters.filetype == PLOT_FILETYPE_AUTO && p >= 4 &&
+-	     plotParameters.filename.substr(p-4,4) == QLatin1String(".eps")) ||
++	     plotParameters.filename.substr(p-4,4) == basic_string<char>(".eps")) ||
+ 	    (plotParameters.filetype == PLOT_FILETYPE_AUTO && p >= 3 &&
+-	     plotParameters.filename.substr(p-3,3) == QLatin1String(".ps")))
++	     plotParameters.filename.substr(p-3,3) == basic_string<char>(".ps")))
+ 	    setResult(new Cantor::EpsResult(KUrl(plotParameters.filename.c_str())));
+ 	else
+ 	    setResult(new Cantor::ImageResult(KUrl(plotParameters.filename.c_str())));
+-- 
+2.5.0
+
diff --git a/pkgs/applications/kde-apps-15.04/default.nix b/pkgs/applications/kde-apps-15.04/default.nix
index 5c36b735338..83aca36bc00 100644
--- a/pkgs/applications/kde-apps-15.04/default.nix
+++ b/pkgs/applications/kde-apps-15.04/default.nix
@@ -223,6 +223,10 @@ let
         '';
       };
 
+      cantor = extendDerivation (kde4Package super.cantor) {
+        patches = [ ./cantor/0001-qalculate-filename-string-type.patch ];
+      };
+
       cervisia = kde4Package super.cervisia;
 
       dolphin-plugins = kde4Package super.dolphin-plugins;