diff --git a/modules/gmake2/gmake2.lua b/modules/gmake2/gmake2.lua
index e9d79e95..3267b161 100644
--- a/modules/gmake2/gmake2.lua
+++ b/modules/gmake2/gmake2.lua
@@ -231,17 +231,31 @@
 			p.outln('')
 		end
 
+		local first = true
 		for cfg in project.eachconfig(prj) do
 			local settings = table.difference(root[cfg], root.settings)
 			if #settings > 0 then
-				_x('ifeq ($(config),%s)', cfg.shortname)
+				if first then
+					_x('ifeq ($(config),%s)', cfg.shortname)
+					first = false
+				else
+					_x('else ifeq ($(config),%s)', cfg.shortname)
+				end
+
 				for k, v in ipairs(settings) do
 					p.outln(v)
 				end
-				p.outln('endif')
-				p.outln('')
+
+				_p('')
 			end
 		end
+
+		if not first then
+			p.outln('else')
+			p.outln('  $(error "invalid configuration $(config)")')
+			p.outln('endif')
+			p.outln('')
+		end
 	end
 
 
diff --git a/modules/gmake2/gmake2_makefile.lua b/modules/gmake2/gmake2_makefile.lua
index f6f53e9e..cf70535c 100644
--- a/modules/gmake2/gmake2_makefile.lua
+++ b/modules/gmake2/gmake2_makefile.lua
@@ -47,6 +47,7 @@
 	end
 
 	function makefile.configs(prj)
+		local first = true
 		for cfg in project.eachconfig(prj) do
 			-- identify the toolset used by this configurations (would be nicer if
 			-- this were computed and stored with the configuration up front)
@@ -56,8 +57,20 @@
 				error("Invalid toolset '" .. cfg.toolset .. "'")
 			end
 
-			_x('ifeq ($(config),%s)', cfg.shortname)
+			if first then
+				_x('ifeq ($(config),%s)', cfg.shortname)
+				first = false
+			else
+				_x('else ifeq ($(config),%s)', cfg.shortname)
+			end
+
 			p.callarray(make, makefile.elements.configuration, cfg, toolset)
+			_p('')
+		end
+
+		if not first then
+			_p('else')
+			_p('  $(error "invalid configuration $(config)")')
 			_p('endif')
 			_p('')
 		end
diff --git a/modules/gmake2/gmake2_workspace.lua b/modules/gmake2/gmake2_workspace.lua
index 7b310a09..a8a25920 100644
--- a/modules/gmake2/gmake2_workspace.lua
+++ b/modules/gmake2/gmake2_workspace.lua
@@ -37,17 +37,31 @@
 --
 
 	function gmake2.configmap(wks)
+		local first = true
 		for cfg in p.workspace.eachconfig(wks) do
-			_p('ifeq ($(config),%s)', cfg.shortname)
+			if first then
+				_p('ifeq ($(config),%s)', cfg.shortname)
+				first = false
+			else
+				_p('else ifeq ($(config),%s)', cfg.shortname)
+			end
+
 			for prj in p.workspace.eachproject(wks) do
 				local prjcfg = project.getconfig(prj, cfg.buildcfg, cfg.platform)
 				if prjcfg then
 					_p('  %s_config = %s', gmake2.tovar(prj.name), prjcfg.shortname)
 				end
 			end
-			_p('endif')
+
+			_p('')
+		end
+
+		if not first then
+			_p('else')
+			_p('  $(error "invalid configuration $(config)")')
+			_p('endif')
+			_p('')
 		end
-		_p('')
 	end
 
 
diff --git a/modules/gmake2/tests/test_gmake2_file_rules.lua b/modules/gmake2/tests/test_gmake2_file_rules.lua
index fb23af32..a6137465 100644
--- a/modules/gmake2/tests/test_gmake2_file_rules.lua
+++ b/modules/gmake2/tests/test_gmake2_file_rules.lua
@@ -121,13 +121,15 @@ obj/Debug/hello.obj: hello.x
 	@echo Compiling hello.x
 	$(SILENT) cxc -c "hello.x" -o "obj/Debug/hello.xo"
 	$(SILENT) c2o -c "obj/Debug/hello.xo" -o "obj/Debug/hello.obj"
-endif
 
-ifeq ($(config),release)
+else ifeq ($(config),release)
 obj/Release/hello.obj: hello.x
 	@echo Compiling hello.x
 	$(SILENT) cxc -c "hello.x" -o "obj/Release/hello.xo"
 	$(SILENT) c2o -c "obj/Release/hello.xo" -o "obj/Release/hello.obj"
+
+else
+  $(error "invalid configuration $(config)")
 endif
 		]]
 	end
@@ -152,13 +154,15 @@ obj/Debug/hello.obj: hello.x hello.x.inc hello.x.inc2
 	@echo Compiling hello.x
 	$(SILENT) cxc -c "hello.x" -o "obj/Debug/hello.xo"
 	$(SILENT) c2o -c "obj/Debug/hello.xo" -o "obj/Debug/hello.obj"
-endif
 
-ifeq ($(config),release)
+else ifeq ($(config),release)
 obj/Release/hello.obj: hello.x hello.x.inc hello.x.inc2
 	@echo Compiling hello.x
 	$(SILENT) cxc -c "hello.x" -o "obj/Release/hello.xo"
 	$(SILENT) c2o -c "obj/Release/hello.xo" -o "obj/Release/hello.obj"
+
+else
+  $(error "invalid configuration $(config)")
 endif
 		]]
 	end
diff --git a/modules/gmake2/tests/test_gmake2_objects.lua b/modules/gmake2/tests/test_gmake2_objects.lua
index 44b2d3b5..73592c47 100644
--- a/modules/gmake2/tests/test_gmake2_objects.lua
+++ b/modules/gmake2/tests/test_gmake2_objects.lua
@@ -86,10 +86,12 @@ OBJECTS :=
 
 ifeq ($(config),debug)
 OBJECTS += $(OBJDIR)/hello_debug.o
-endif
 
-ifeq ($(config),release)
+else ifeq ($(config),release)
 OBJECTS += $(OBJDIR)/hello_release.o
+
+else
+  $(error "invalid configuration $(config)")
 endif
 
 		]]
@@ -138,10 +140,12 @@ CUSTOM :=
 
 ifeq ($(config),debug)
 CUSTOM += obj/Debug/hello.luac
-endif
 
-ifeq ($(config),release)
+else ifeq ($(config),release)
 CUSTOM += obj/Release/hello.luac
+
+else
+  $(error "invalid configuration $(config)")
 endif
 		]]
 	end
@@ -170,10 +174,12 @@ OBJECTS :=
 
 ifeq ($(config),debug)
 OBJECTS += obj/Debug/hello.obj
-endif
 
-ifeq ($(config),release)
+else ifeq ($(config),release)
 OBJECTS += obj/Release/hello.obj
+
+else
+  $(error "invalid configuration $(config)")
 endif
 		]]
 	end
@@ -203,10 +209,12 @@ OBJECTS :=
 
 ifeq ($(config),debug)
 OBJECTS += obj/Debug/hello.obj
-endif
 
-ifeq ($(config),release)
+else ifeq ($(config),release)
 OBJECTS += obj/Release/hello.obj
+
+else
+  $(error "invalid configuration $(config)")
 endif
 		]]
 	end
@@ -236,10 +244,12 @@ CUSTOM :=
 
 ifeq ($(config),debug)
 CUSTOM += obj/Debug/hello.obj
-endif
 
-ifeq ($(config),release)
+else ifeq ($(config),release)
 CUSTOM += obj/Release/hello.obj
+
+else
+  $(error "invalid configuration $(config)")
 endif
 		]]
 	end
@@ -262,6 +272,9 @@ OBJECTS :=
 
 ifeq ($(config),release)
 OBJECTS += $(OBJDIR)/hello.o
+
+else
+  $(error "invalid configuration $(config)")
 endif
 
 		]]
@@ -280,6 +293,9 @@ OBJECTS :=
 
 ifeq ($(config),release)
 OBJECTS += $(OBJDIR)/hello.o
+
+else
+  $(error "invalid configuration $(config)")
 endif
 
 		]]