diff --git a/rtdata/languages/Francais b/rtdata/languages/Francais
index 747e80bf0..63a3f2b38 100644
--- a/rtdata/languages/Francais
+++ b/rtdata/languages/Francais
@@ -710,8 +710,9 @@ PREFERENCES_CIEART_LABEL;Utilise la précision float au lieu de double pour CIEC
 PREFERENCES_CIEART_TOOLTIP;Si activé, les calculs CIECAM sont réalisés en précision float au lieu de précision double. Cela amène un léger accroissement de vitesse, et une légère réduction de qualité
 PREFERENCES_CLIPPINGIND;Indication du dépassement de plage dynamique
 PREFERENCES_CMETRICINTENT;Intention Colorimétrique
-PREFERENCES_CUSTPROFBUILDHINT;Fichier éxecutable (ou script) appelé lorsqu'un nouveau profil initial doit être généré pour une image.\nParamètres de ligne de commande pour permettre la génération d'un .pp3 basé sur des règles:\n[Chemin vers le fichier RAW/JPG] [Chemin vers le profil par défault] [ouverture f] [tps d'exposition en seconde] [longueur focale en mm] [ISO] [Objectif] [Appareil photo]
-PREFERENCES_CUSTPROFBUILDPATH;Chemin de l'exécutable
+PREFERENCES_CUSTPROFBUILDHINT;Fichier éxecutable (ou script) appelé lorsqu'un nouveau profil initial doit être généré pour une image.\nParamètres de ligne de commande pour permettre la génération d'un .pp3 basé sur des règles:\n[Chemin vers le fichier RAW/JPG] [Chemin vers le profil par défault] [Chemin de le répertoire Cache de RT] [ouverture f] [tps d'exposition en seconde] [longueur focale en mm] [ISO] [Objectif] [Fabricant de l'appareil photo] [Modèle de l'appareil photo]\n\n<b>ATTENTION:</b> Il vous appartient d'utiliser ou non des guillemts double pour spécifier des chemins si ceux-ci contiennent des espaces
+REFERENCES_CUSTPROFBUILDPATH;Chemin de l'exécutable
+PREFERENCES_CUSTPROFBUILDPATH_TOOLTIP;
 PREFERENCES_CUSTPROFBUILD;Constructeur de profil d'image personnalisé
 PREFERENCES_CUTOVERLAYBRUSH;Masque de recadrage
 PREFERENCES_D50;5000K
diff --git a/rtdata/languages/default b/rtdata/languages/default
index d6f4fee0a..bc446c6f9 100644
--- a/rtdata/languages/default
+++ b/rtdata/languages/default
@@ -709,7 +709,7 @@ PREFERENCES_CIEART_LABEL;Use float precision instead of double
 PREFERENCES_CIEART_TOOLTIP;If enabled, CIECAM02 calculations are performed in the single-precision floating-point format instead of the double-precision one. This provides a small increase in speed at the expense of a negligible loss of quality
 PREFERENCES_CLIPPINGIND;Clipping Indication
 PREFERENCES_CMETRICINTENT;Colorimetric intent
-PREFERENCES_CUSTPROFBUILDHINT;Executable (or script) file called when a new initial processing profile should be generated for an image.\nReceives command line parameters to allow a rules-based processing profile generation:\n[raw/JPG path] [default processing profile path] [f-number] [exposure in secs] [focal length in mm] [ISO] [lens] [camera]
+PREFERENCES_CUSTPROFBUILDHINT;Executable (or script) file called when a new initial processing profile should be generated for an image.\nReceives command line parameters to allow a rules-based processing profile generation:\n[raw/JPG path] [default processing profile path] [RT's cache folder path] [f-number] [exposure in secs] [focal length in mm] [ISO] [lens] [camera make] [camera model]\n\n<b>WARNING:</b> You are responsible of using double quotes where necessary if you're using paths containing spaces.
 PREFERENCES_CUSTPROFBUILDPATH;Executable path
 PREFERENCES_CUSTPROFBUILD;Custom Processing Profile Builder
 PREFERENCES_CUTOVERLAYBRUSH;Crop mask color/transparency
diff --git a/rtgui/options.cc b/rtgui/options.cc
index ca9f352ec..df53b7ed7 100644
--- a/rtgui/options.cc
+++ b/rtgui/options.cc
@@ -1083,34 +1083,34 @@ void Options::load () {
 
         if (SHGetSpecialFolderPathW(NULL,pathW,CSIDL_LOCAL_APPDATA,false)) {
             WideCharToMultiByte(CP_UTF8,0,pathW,-1,pathA,MAX_PATH,0,0);
-            rtdir = Glib::ustring(pathA) + Glib::ustring("\\") + Glib::ustring(CACHEFOLDERNAME);
+            rtdir = Glib::build_filename(Glib::ustring(pathA), Glib::ustring(CACHEFOLDERNAME));
 		}
 	}
 #else
-    rtdir = Glib::ustring(g_get_user_config_dir ()) + Glib::ustring("/") + Glib::ustring(CACHEFOLDERNAME);
+    rtdir = Glib::build_filename(Glib::ustring(g_get_user_config_dir ()), Glib::ustring(CACHEFOLDERNAME));
 #endif
 
     // Set the cache folder in RT's base folder
-    cacheBaseDir = argv0 + "/cache";
+    cacheBaseDir = Glib::build_filename(argv0, "cache");
 
     // Read the global option file (the one located in the application's base folder)
-    options.readFromFile (argv0+"/options");
+    options.readFromFile (Glib::build_filename(argv0, "options"));
 
     // Check if RT is installed in Multi-User mode
     if (options.multiUser) {
         // Read the user option file (the one located somewhere in the user's home folder)
         // Those values supersets those of the global option file
-        int r = options.readFromFile (rtdir + "/options");
+        int r = options.readFromFile (Glib::build_filename(rtdir, "options"));
         // If the local option file does not exist or is broken, and the local cache folder does not exist, recreate it
         if (r && !safe_g_mkdir_with_parents (rtdir, 511)) {
             // Save the option file
-            options.saveToFile (rtdir + "/options");
+            options.saveToFile (Glib::build_filename(rtdir, "options"));
         }
         // Modify the path of the cache folder to the user's personal folder
 #ifdef WIN32
-        cacheBaseDir = rtdir + "/cache";
+        cacheBaseDir = Glib::build_filename(rtdir, "cache");
 #else
-        cacheBaseDir = Glib::ustring(g_get_user_cache_dir()) + Glib::ustring("/") + Glib::ustring(CACHEFOLDERNAME);
+        cacheBaseDir = Glib::build_filename(Glib::ustring(g_get_user_cache_dir()), Glib::ustring(CACHEFOLDERNAME));
 #endif
     }
 
@@ -1185,10 +1185,10 @@ void Options::load () {
 void Options::save () {
 
     if (options.multiUser==false) {
-        options.saveToFile (argv0+"/options");
+        options.saveToFile (Glib::build_filename(argv0, "options"));
     }
     else {
-        options.saveToFile (rtdir + "/options");
+        options.saveToFile (Glib::build_filename(rtdir, "options"));
     }
 }
 
diff --git a/rtgui/thumbnail.cc b/rtgui/thumbnail.cc
index 5d6e0bd6e..0544aea2f 100644
--- a/rtgui/thumbnail.cc
+++ b/rtgui/thumbnail.cc
@@ -205,7 +205,7 @@ rtengine::procparams::ProcParams* Thumbnail::createProcParamsForUpdate(bool retu
     Glib::ustring defaultPparamsPath = options.findProfilePath(defProf);
     if (!options.customProfileBuilder.empty() && !defaultPparamsPath.empty() && (!hasProcParams() || forceCPB) && cfs && cfs->exifValid) {
         // For the filename etc. do NOT use streams, since they are not UTF8 safe
-        Glib::ustring cmdLine=Glib::ustring("\"") + options.customProfileBuilder + Glib::ustring("\" \"") + fname + Glib::ustring("\" \"")
+        Glib::ustring cmdLine = options.customProfileBuilder + Glib::ustring(" \"") + fname + Glib::ustring("\" \"")
         + (defaultPparamsPath == DEFPROFILE_INTERNAL ? "Neutral" : Glib::build_filename(defaultPparamsPath, Glib::path_get_basename(defProf) + paramFileExtension)) + Glib::ustring("\" ");
 
         // ustring doesn't know int etc formatting, so take these via (unsafe) stream