diff --git a/util/interpolation.lua b/util/interpolation.lua
index 37d5610f..3f351952 100644
--- a/util/interpolation.lua
+++ b/util/interpolation.lua
@@ -64,23 +64,14 @@ end
 
 local FRAMES = {}
 
-function push_frame()
-    local frame = {}
+function push_frame(frame)
     table.insert(FRAMES, frame)
-    return frame
 end
 
 function pop_frame()
     table.remove(FRAMES)
 end
 
-function adjust_frame(t)
-    local last_frame = FRAMES[#FRAMES]
-    for k, v in pairs(t) do
-        last_frame[k] = v
-    end
-end
-
 function print_frame()
     local last_frame = FRAMES[#FRAMES]
     for k, v in pairs(last_frame) do
@@ -107,15 +98,15 @@ function expand(str)
 end
 
 function with_rep(vars, f)
-    push_frame()
-    adjust_frame(vars)
+    push_frame(vars)
     local ret = f()
     pop_frame()
     return ret
 end
 
 function iter_rep(varspec, f)
-    local frame = push_frame()
+    local frame = {}
+    push_frame(frame)
     local keys = table_keys(varspec)
     local function loop(i)
         if #keys + 1 == i then
diff --git a/util/tup-ext.lua b/util/tup-ext.lua
index bc20554a..524d90dc 100644
--- a/util/tup-ext.lua
+++ b/util/tup-ext.lua
@@ -43,7 +43,8 @@ function glob(pat, opts)
     local key = opts and opts.key
     local seen = {}
     for pat in iter(globpat_normalize(pat)) do
-        local frame = push_frame()
+        local frame = {}
+        push_frame(frame)
         for file in iter(tup.glob(pat)) do
             -- Workaround a weird issue pre reported
             file = file:gsub("//", "/")
@@ -112,7 +113,8 @@ local function do_rule_frame(opts, foreach)
     if foreach then
         local input = glob(opts.input, opts)
         for i in iter(input) do
-            local frame = push_frame()
+            local frame = {}
+            push_frame(frame)
             frame.input = i
             local output = {}
             for v in iter(astable(opts.output)) do
@@ -123,7 +125,8 @@ local function do_rule_frame(opts, foreach)
             pop_frame()
         end
     else
-        local frame = push_frame()
+        local frame = {}
+        push_frame(frame)
         local input = glob(opts.input)
         frame.input = tostring(input)
         local output = {}