diff --git a/first/ackbuilder.lua b/first/ackbuilder.lua
index 7bbf2ee04..c7798e6b8 100644
--- a/first/ackbuilder.lua
+++ b/first/ackbuilder.lua
@@ -114,13 +114,13 @@ local function concatpath(...)
 	return (p:gsub("/+", "/"):gsub("^%./", ""):gsub("/%./", "/"))
 end
 
--- Turns a list of strings or targets into a list of targets, expanding
--- recursive lists and wildcards.
+-- Returns a list of the targets within the given collection; the keys of any
+-- keyed items are lost. Lists and wildcards are expanded.
 local function targetsof(...)
 	local o = {}
 
 	local function process(items)
-		for _, item in ipairs(items) do
+		for _, item in pairs(items) do
 			if (type(item) == "table") then
 				if item.is then
 					-- This is a target.
@@ -430,7 +430,23 @@ local typeconverters = {
 		elseif (type(i) ~= "table") then
 			error(string.format("property '%s' must be a target list", propname))
 		end
-		return targetsof(i)
+
+		local m = {}
+		for k, v in pairs(i) do
+			local ts = targetsof(v)
+			if (type(k) == "number") then
+				for _, t in ipairs(ts) do
+					m[#m+1] = t
+				end
+			else
+				if (#ts ~= 1) then
+					error(string.format("named target '%s' can only be assigned from a single target", k))
+				else
+					m[k] = ts[1]
+				end
+			end
+		end
+		return m
 	end,
 
 	strings = function(propname, i)
@@ -653,7 +669,7 @@ definerule("simplerule",
 
 definerule("installable",
 	{
-		map = { type="table", default={} },
+		map = { type="targets", default={} },
 	},
 	function (e)
 		local deps = {}
@@ -661,12 +677,6 @@ definerule("installable",
 		local srcs = {}
 		local dests = {}
 		for dest, src in pairs(e.map) do
-			src = targetsof(src)
-			if (#src ~= 1) then
-				error("installable can only cope with one target at a time")
-			end
-			src = src[1]
-
 			if src.is.installable then
 				if (type(dest) ~= "number") then
 					error("can't specify a destination filename when installing an installable")
diff --git a/first/build.lua b/first/build.lua
index 9bbb905a9..0efdadb12 100644
--- a/first/build.lua
+++ b/first/build.lua
@@ -170,27 +170,44 @@ definerule("clibrary",
 			}
 		end
 
-		local hdrs = filenamesof(e.hdrs)
-
 		local commands = {}
-		for _, s in ipairs(e.commands) do
-			commands[#commands+1] = s
+		local outleaves = {}
+		if (#e.srcs > 0) then
+			for _, s in ipairs(e.commands) do
+				commands[#commands+1] = s
+			end
+			outleaves[#outleaves+1] = e.name..".a"
 		end
-		if (#hdrs > 0) then
-			commands[#commands+1] = "cp %{hdrs} %{dir}"
+
+		local hdrsin = {}
+		for dest, src in pairs(e.hdrs) do
+			if (type(dest) == "number") then
+				for _, f in ipairs(filenamesof(src)) do
+					hdrsin[#hdrsin+1] = f
+					outleaves[#outleaves+1] = basename(f)
+					commands[#commands+1] = "cp "..asstring(f).." %{dir}"
+				end
+			else
+				local fs = filenamesof(src)
+				if (#fs ~= 1) then
+					error(string.format("keyed header '%s' can only be a single file", dest))
+				end
+				local f = fs[1]
+
+				hdrsin[#hdrsin+1] = f
+				outleaves[#outleaves+1] = dest
+				commands[#commands+1] = "cp "..asstring(f).." %{dir}/"..dest
+			end
 		end
 
 		return normalrule {
 			name = e.name,
 			cwd = e.cwd,
 			ins = ins,
-			deps = concat(e.hdrs, e.deps),
-			outleaves = concat(e.name..".a", basename(hdrs)),
+			deps = {hdrsin, e.deps},
+			outleaves = outleaves,
 			label = e.label,
 			commands = commands,
-			vars = {
-				hdrs = hdrs
-			}
 		}
 	end
 )