diff --git a/lang/m2/comp/build.lua b/lang/m2/comp/build.lua
index 4e12d24f7..490947508 100644
--- a/lang/m2/comp/build.lua
+++ b/lang/m2/comp/build.lua
@@ -31,8 +31,8 @@ normalrule {
 	}
 }
 
-for _, f in ipairs(filenamesof("./*.H")) do
-	local name = replace(basename(f), "%.H$", "")
+for _, f in ipairs(filenamesof("./*.xh")) do
+	local name = replace(basename(f), "%.xh$", "")
 	normalrule {
 		name = name.."_h",
 		ins = {
@@ -46,8 +46,8 @@ for _, f in ipairs(filenamesof("./*.H")) do
 	}
 end
 
-for _, f in ipairs(filenamesof("./*.C")) do
-	local name = replace(basename(f), "%.C$", "")
+for _, f in ipairs(filenamesof("./*.xc")) do
+	local name = replace(basename(f), "%.xc$", "")
 	normalrule {
 		name = name.."_c",
 		ins = {
@@ -65,8 +65,8 @@ normalrule {
 	name = "next_c",
 	ins = {
 		"./make.next",
-		"./*.H",
-		"./*.C",
+		"./*.xh",
+		"./*.xc",
 	},
 	outleaves = { "next.c" },
 	commands = {
diff --git a/lang/m2/comp/casestat.C b/lang/m2/comp/casestat.xc
similarity index 100%
rename from lang/m2/comp/casestat.C
rename to lang/m2/comp/casestat.xc
diff --git a/lang/m2/comp/def.H b/lang/m2/comp/def.xh
similarity index 100%
rename from lang/m2/comp/def.H
rename to lang/m2/comp/def.xh
diff --git a/lang/m2/comp/node.H b/lang/m2/comp/node.xh
similarity index 100%
rename from lang/m2/comp/node.H
rename to lang/m2/comp/node.xh
diff --git a/lang/m2/comp/real.H b/lang/m2/comp/real.xh
similarity index 100%
rename from lang/m2/comp/real.H
rename to lang/m2/comp/real.xh
diff --git a/lang/m2/comp/scope.C b/lang/m2/comp/scope.xc
similarity index 100%
rename from lang/m2/comp/scope.C
rename to lang/m2/comp/scope.xc
diff --git a/lang/m2/comp/tmpvar.C b/lang/m2/comp/tmpvar.xc
similarity index 100%
rename from lang/m2/comp/tmpvar.C
rename to lang/m2/comp/tmpvar.xc
diff --git a/lang/m2/comp/type.H b/lang/m2/comp/type.xh
similarity index 100%
rename from lang/m2/comp/type.H
rename to lang/m2/comp/type.xh
diff --git a/lang/pc/comp/build.lua b/lang/pc/comp/build.lua
index a2cb9accb..c10c1793f 100644
--- a/lang/pc/comp/build.lua
+++ b/lang/pc/comp/build.lua
@@ -31,8 +31,8 @@ normalrule {
 	}
 }
 
-for _, f in ipairs(filenamesof("./*.H")) do
-	local name = replace(basename(f), "%.H$", "")
+for _, f in ipairs(filenamesof("./*.xh")) do
+	local name = replace(basename(f), "%.xh$", "")
 	normalrule {
 		name = name.."_h",
 		ins = {
@@ -46,8 +46,8 @@ for _, f in ipairs(filenamesof("./*.H")) do
 	}
 end
 
-for _, f in ipairs(filenamesof("./*.C")) do
-	local name = replace(basename(f), "%.C$", "")
+for _, f in ipairs(filenamesof("./*.xc")) do
+	local name = replace(basename(f), "%.xc$", "")
 	normalrule {
 		name = name.."_c",
 		ins = {
@@ -65,8 +65,8 @@ normalrule {
 	name = "next_c",
 	ins = {
 		"./make.next",
-		"./*.H",
-		"./*.C",
+		"./*.xh",
+		"./*.xc",
 	},
 	outleaves = { "next.c" },
 	commands = {
diff --git a/lang/pc/comp/casestat.C b/lang/pc/comp/casestat.xc
similarity index 100%
rename from lang/pc/comp/casestat.C
rename to lang/pc/comp/casestat.xc
diff --git a/lang/pc/comp/def.H b/lang/pc/comp/def.xh
similarity index 100%
rename from lang/pc/comp/def.H
rename to lang/pc/comp/def.xh
diff --git a/lang/pc/comp/desig.H b/lang/pc/comp/desig.xh
similarity index 100%
rename from lang/pc/comp/desig.H
rename to lang/pc/comp/desig.xh
diff --git a/lang/pc/comp/node.H b/lang/pc/comp/node.xh
similarity index 100%
rename from lang/pc/comp/node.H
rename to lang/pc/comp/node.xh
diff --git a/lang/pc/comp/scope.H b/lang/pc/comp/scope.xh
similarity index 100%
rename from lang/pc/comp/scope.H
rename to lang/pc/comp/scope.xh
diff --git a/lang/pc/comp/tmpvar.C b/lang/pc/comp/tmpvar.xc
similarity index 100%
rename from lang/pc/comp/tmpvar.C
rename to lang/pc/comp/tmpvar.xc
diff --git a/lang/pc/comp/type.H b/lang/pc/comp/type.xh
similarity index 100%
rename from lang/pc/comp/type.H
rename to lang/pc/comp/type.xh