diff --git a/lib/lyx2lyx/lyx_2_1.py b/lib/lyx2lyx/lyx_2_1.py
index 133d500f9f..d370112aa5 100644
--- a/lib/lyx2lyx/lyx_2_1.py
+++ b/lib/lyx2lyx/lyx_2_1.py
@@ -353,7 +353,7 @@ def revert_undertilde(document):
 
 
 def revert_negative_space(document):
-    "Revert InsetSpace negmedspace and negthickspace into its TeX-code counterpart"
+    "Revert InsetSpace negmedspace and negthickspace into their TeX-code counterparts"
     i = 0
     j = 0
     reverted = False
@@ -366,7 +366,7 @@ def revert_negative_space(document):
           if reverted == True:
             i = find_token(document.header, "\\use_amsmath 2", 0)
             if i == -1:
-              add_to_preamble(document, ["\\@ifundefined{negthickspace}{\\usepackage{amsmath}}"])
+              add_to_preamble(document, ["\\@ifundefined{negthickspace}{\\usepackage{amsmath}}{}"])
           return
       if i == -1:
         return
diff --git a/lib/lyx2lyx/lyx_2_4.py b/lib/lyx2lyx/lyx_2_4.py
index 206365185e..f778b4aea7 100644
--- a/lib/lyx2lyx/lyx_2_4.py
+++ b/lib/lyx2lyx/lyx_2_4.py
@@ -3753,6 +3753,28 @@ def revert_counter_inset(document):
     if pretext:
         add_to_preamble(document, pretext)
 
+
+def revert_ams_spaces(document):
+    "Revert InsetSpace medspace and thickspace into their TeX-code counterparts"
+    Found = False
+    insets = ["\\medspace{}", "\\thickspace{}"]
+    for inset in insets:
+        i = 0
+        j = 0
+        i = find_token(document.body, "\\begin_inset space " + inset, i)
+        if i == -1:
+            continue
+        end = find_end_of_inset(document.body, i)
+        subst = put_cmd_in_ert(inset)
+        document.body[i : end + 1] = subst
+        Found = True
+      
+    if Found == True:
+        # load amsmath in the preamble if not already loaded
+        i = find_token(document.header, "\\use_package amsmath 2", 0)
+        if i == -1:
+            add_to_preamble(document, ["\\@ifundefined{thickspace}{\\usepackage{amsmath}}{}"])
+            return
         
 ##
 # Conversion hub
@@ -3809,10 +3831,12 @@ convert = [
            [591, [convert_postpone_fragile]],
            [592, []],
            [593, [convert_counter_maintenance]],
-           [594, []]
+           [594, []],
+           [595, []]
           ]
 
-revert =  [[593, [revert_counter_inset]],
+revert =  [[594, [revert_ams_spaces]],
+           [593, [revert_counter_inset]],
            [592, [revert_counter_maintenance]],
            [591, [revert_colrow_tracking]],
            [590, [revert_postpone_fragile]],
diff --git a/lib/ui/stdcontext.inc b/lib/ui/stdcontext.inc
index 120aac4dd9..2c28a85606 100644
--- a/lib/ui/stdcontext.inc
+++ b/lib/ui/stdcontext.inc
@@ -244,6 +244,8 @@ Menuset
 		Item "Protected Space|o" "inset-modify space ~"
 		Item "Visible Space|a" "inset-modify space \textvisiblespace{}"
 		Item "Thin Space|T" "inset-modify space \thinspace{}"
+		Item "Medium Space|M" "inset-modify space \medspace{}"
+		Item "Thick Space|i" "inset-modify space \thickspace{}"
 		Item "Negative Thin Space|N" "inset-modify space \negthinspace{}"
 		Item "Negative Medium Space|v" "inset-modify space \negmedspace{}"
 		Item "Negative Thick Space|h" "inset-modify space \negthickspace{}"
@@ -252,7 +254,7 @@ Menuset
 		Item "Quad Space|Q" "inset-modify space \quad{}"
 		Item "Double Quad Space|u" "inset-modify space \qquad{}"
 		Item "Horizontal Fill|F" "inset-modify space \hfill{}"
-		Item "Protected Horizontal Fill|i" "inset-modify space \hspace*{\fill}"
+		Item "Protected Horizontal Fill|z" "inset-modify space \hspace*{\fill}"
 		Item "Horizontal Fill (Dots)|D" "inset-modify space \dotfill{}"
 		Item "Horizontal Fill (Rule)|R" "inset-modify space \hrulefill{}"
 		Item "Horizontal Fill (Left Arrow)|L" "inset-modify space \leftarrowfill{}"
diff --git a/src/frontends/qt/GuiHSpace.cpp b/src/frontends/qt/GuiHSpace.cpp
index 4307ae0e0f..9a1437009b 100644
--- a/src/frontends/qt/GuiHSpace.cpp
+++ b/src/frontends/qt/GuiHSpace.cpp
@@ -41,32 +41,20 @@ GuiHSpace::GuiHSpace(bool math_mode, QWidget * parent)
 	setupUi(this);
 
 	spacingCO->clear();
-	if (math_mode_) {
-		spacingCO->addItem(qt_("Interword Space"), "normal");
-		spacingCO->addItem(qt_("Thin Space"), "thinspace");
-		spacingCO->addItem(qt_("Medium Space"), "medspace");
-		spacingCO->addItem(qt_("Thick Space"), "thickspace");
-		spacingCO->addItem(qt_("Negative Thin Space"), "negthinspace");
-		spacingCO->addItem(qt_("Negative Medium Space"), "negmedspace");
-		spacingCO->addItem(qt_("Negative Thick Space"), "negthickspace");
-		spacingCO->addItem(qt_("Half Quad (0.5 em)"), "halfquad");
-		spacingCO->addItem(qt_("Quad (1 em)"), "quad");
-		spacingCO->addItem(qt_("Double Quad (2 em)"), "qquad");
-		spacingCO->addItem(qt_("Horizontal Fill"), "hfill");
-		spacingCO->addItem(qt_("Custom"), "custom");
-	} else {
-		spacingCO->addItem(qt_("Interword Space"), "normal");
-		spacingCO->addItem(qt_("Thin Space"), "thinspace");
-		spacingCO->addItem(qt_("Negative Thin Space"), "negthinspace");
-		spacingCO->addItem(qt_("Negative Medium Space"), "negmedspace");
-		spacingCO->addItem(qt_("Negative Thick Space"), "negthickspace");
-		spacingCO->addItem(qt_("Half Quad (0.5 em)"), "halfquad");
-		spacingCO->addItem(qt_("Quad (1 em)"), "quad");
-		spacingCO->addItem(qt_("Double Quad (2 em)"), "qquad");
-		spacingCO->addItem(qt_("Horizontal Fill"), "hfill");
-		spacingCO->addItem(qt_("Custom"), "custom");
+	spacingCO->addItem(qt_("Interword Space"), "normal");
+	spacingCO->addItem(qt_("Thin Space"), "thinspace");
+	spacingCO->addItem(qt_("Medium Space"), "medspace");
+	spacingCO->addItem(qt_("Thick Space"), "thickspace");
+	spacingCO->addItem(qt_("Negative Thin Space"), "negthinspace");
+	spacingCO->addItem(qt_("Negative Medium Space"), "negmedspace");
+	spacingCO->addItem(qt_("Negative Thick Space"), "negthickspace");
+	spacingCO->addItem(qt_("Half Quad (0.5 em)"), "halfquad");
+	spacingCO->addItem(qt_("Quad (1 em)"), "quad");
+	spacingCO->addItem(qt_("Double Quad (2 em)"), "qquad");
+	spacingCO->addItem(qt_("Horizontal Fill"), "hfill");
+	if (!math_mode_)
 		spacingCO->addItem(qt_("Visible Space"), "visible");
-	}
+	spacingCO->addItem(qt_("Custom"), "custom");
 
 	connect(spacingCO, SIGNAL(highlighted(QString)),
 		this, SLOT(changedSlot()));
diff --git a/src/insets/InsetSpace.cpp b/src/insets/InsetSpace.cpp
index 799568eadd..84c6a2599c 100644
--- a/src/insets/InsetSpace.cpp
+++ b/src/insets/InsetSpace.cpp
@@ -516,9 +516,9 @@ void InsetSpaceParams::read(Lexer & lex)
 		kind = InsetSpaceParams::VISIBLE;
 	else if (command == "\\thinspace{}")
 		kind = InsetSpaceParams::THIN;
-	else if (math && command == "\\medspace{}")
+	else if (command == "\\medspace{}")
 		kind = InsetSpaceParams::MEDIUM;
-	else if (math && command == "\\thickspace{}")
+	else if (command == "\\thickspace{}")
 		kind = InsetSpaceParams::THICK;
 	else if (command == "\\quad{}")
 		kind = InsetSpaceParams::QUAD;
@@ -597,10 +597,16 @@ void InsetSpace::latex(otexstream & os, OutputParams const & runparams) const
 		os << (runparams.free_spacing ? " " : "\\,");
 		break;
 	case InsetSpaceParams::MEDIUM:
-		os << (runparams.free_spacing ? " " : "\\:");
+		if (params_.math)
+			os << (runparams.free_spacing ? " " : "\\:");
+		else
+			os << (runparams.free_spacing ? " " : "\\medspace{}");
 		break;
 	case InsetSpaceParams::THICK:
-		os << (runparams.free_spacing ? " " : "\\;");
+		if (params_.math)
+			os << (runparams.free_spacing ? " " : "\\;");
+		else
+			os << (runparams.free_spacing ? " " : "\\thickspace{}");
 		break;
 	case InsetSpaceParams::QUAD:
 		os << (runparams.free_spacing ? " " : "\\quad{}");
@@ -867,8 +873,11 @@ docstring InsetSpace::xhtml(XMLStream & xs, OutputParams const &) const
 
 void InsetSpace::validate(LaTeXFeatures & features) const
 {
-	if (params_.kind == InsetSpaceParams::NEGMEDIUM ||
-	    params_.kind == InsetSpaceParams::NEGTHICK)
+	if ((params_.kind == InsetSpaceParams::NEGMEDIUM
+	     || params_.kind == InsetSpaceParams::NEGTHICK)
+	    || (!params_.math
+		&& (params_.kind == InsetSpaceParams::MEDIUM
+		    || params_.kind == InsetSpaceParams::THICK)))
 		features.require("amsmath");
 }
 
diff --git a/src/tex2lyx/text.cpp b/src/tex2lyx/text.cpp
index d1b35c431e..4053ddbfe9 100644
--- a/src/tex2lyx/text.cpp
+++ b/src/tex2lyx/text.cpp
@@ -318,16 +318,16 @@ char const * const known_tex_extensions[] = {"tex", 0};
 /// spaces known by InsetSpace
 char const * const known_spaces[] = { " ", "space", ",",
 "thinspace", "quad", "qquad", "enspace", "enskip",
-"negthinspace", "negmedspace", "negthickspace", "textvisiblespace",
-"hfill", "dotfill", "hrulefill", "leftarrowfill", "rightarrowfill",
-"upbracefill", "downbracefill", 0};
+"medspace", "thickspace", "negthinspace", "negmedspace", "negthickspace",
+"textvisiblespace", "hfill", "dotfill", "hrulefill", "leftarrowfill",
+"rightarrowfill", "upbracefill", "downbracefill", 0};
 
 /// the same as known_spaces with .lyx names
 char const * const known_coded_spaces[] = { "space{}", "space{}",
 "thinspace{}", "thinspace{}", "quad{}", "qquad{}", "enspace{}", "enskip{}",
-"negthinspace{}", "negmedspace{}", "negthickspace{}", "textvisiblespace{}",
-"hfill{}", "dotfill{}", "hrulefill{}", "leftarrowfill{}", "rightarrowfill{}",
-"upbracefill{}", "downbracefill{}", 0};
+"medspace{}", "thickspace{}", "negthinspace{}", "negmedspace{}", "negthickspace{}",
+"textvisiblespace{}", "hfill{}", "dotfill{}", "hrulefill{}", "leftarrowfill{}",
+"rightarrowfill{}", "upbracefill{}", "downbracefill{}", 0};
 
 /// known TIPA combining diacritical marks
 char const * const known_tipa_marks[] = {"textsubwedge", "textsubumlaut",
diff --git a/src/version.h b/src/version.h
index 866fe10e95..fd40047cf4 100644
--- a/src/version.h
+++ b/src/version.h
@@ -32,8 +32,8 @@ extern char const * const lyx_version_info;
 
 // Do not remove the comment below, so we get merge conflict in
 // independent branches. Instead add your own.
-#define LYX_FORMAT_LYX 594 // rikiheck: counter insets
-#define LYX_FORMAT_TEX2LYX 594
+#define LYX_FORMAT_LYX 595 // spitz: medspace and thickspace
+#define LYX_FORMAT_TEX2LYX 595
 
 #if LYX_FORMAT_TEX2LYX != LYX_FORMAT_LYX
 #ifndef _MSC_VER