diff --git a/Makefile b/Makefile
index dfd1eec..29b3737 100644
--- a/Makefile
+++ b/Makefile
@@ -25,9 +25,9 @@ all: build optimize
 .PHONY: test
 test: build optimize
 	@echo "\033[1;4mRunning unoptimized tests...\033[0m"
-	@$(LUA_BIN) nomsu.lua tools/test.nom $(CORE_NOM_FILES) $(LIB_NOM_FILES)
+	@$(LUA_BIN) nomsu.lua -O0 tools/test.nom $(CORE_NOM_FILES) $(LIB_NOM_FILES)
 	@echo "\n\033[1;4mRunning optimized tests...\033[0m"
-	@$(LUA_BIN) nomsu.lua -O tools/test.nom $(CORE_NOM_FILES) $(LIB_NOM_FILES)
+	@$(LUA_BIN) nomsu.lua -O1 tools/test.nom $(CORE_NOM_FILES) $(LIB_NOM_FILES)
 
 %.lua: %.moon
 	@moonc $<
diff --git a/doc/nomsu.1 b/doc/nomsu.1
index 11439aa..23a3549 100644
--- a/doc/nomsu.1
+++ b/doc/nomsu.1
@@ -33,8 +33,8 @@ Specify the desired Nomsu version (defaults to the latest installed version). E.
 .BI \-L
 List the installed versions of Nomsu (if \fB-V\fR is supplied, only print versions that match the requested pattern).
 .TP
-.B \-O
-Run the compiler in optimized mode (use precompiled .lua versions of .nom files, when available)
+.B \-O " level"
+Run the compiler with the given optimization level (default: 1). If \fBlevel\fR is >0, use precompiled .lua versions of .nom files, when available.
 .TP
 .B \-v
 Verbose: print compiled lua code as it's generated for the input files.
diff --git a/nomsu.lua b/nomsu.lua
index 32592dc..8953e99 100644
--- a/nomsu.lua
+++ b/nomsu.lua
@@ -55,10 +55,10 @@ end
 local EXIT_SUCCESS, EXIT_FAILURE = 0, 1
 local usage = [=[Nomsu Compiler
 
-Usage: (nomsu | lua nomsu.lua | moon nomsu.moon) [-V version] [-O] [-v] [-c] [-s] [-t] [-I file] [--help | -h] [--version] [--no-core] [file [nomsu args...]]
+Usage: (nomsu | lua nomsu.lua | moon nomsu.moon) [-V version] [-O optimization level] [-v] [-c] [-s] [-t] [-I file] [--help | -h] [--version] [--no-core] [file [nomsu args...]]
 
 OPTIONS
-    -O Run the compiler in optimized mode (use precompiled .lua versions of Nomsu files, when available).
+    -O <level> Run the compiler with the given optimization level (>0: use precompiled .lua versions of Nomsu files, when available).
     -v Verbose: print compiled lua code.
     -c Compile the input files into a .lua files.
     -e Execute the specified string.
@@ -96,7 +96,7 @@ local file_queue = { }
 local sep = "\0"
 local parser = re.compile([[    args <- {| (flag %sep)* (({~ file ~} -> add_file) %sep)? {:nomsu_args: {| ({(!%sep .)*} %sep)* |} :} %sep? |} !.
     flag <-
-        {:optimized: ("-O" -> true) :}
+        {:optimization: "-O" (%sep? (([0-9]+) -> tonumber))? :}
       / ("-I" %sep? ({~ file ~} -> add_file))
       / ("-e" %sep? (({} {~ file ~}) -> add_exec_string))
       / ({:check_syntax: ("-s" -> true):})
@@ -110,9 +110,12 @@ local parser = re.compile([[    args <- {| (flag %sep)* (({~ file ~} -> add_file
       / {:requested_version: "-V" (%sep? {([0-9.])+})? :}
     file <- ("-" -> "stdin") / {(!%sep .)+}
 ]], {
-  ["true"] = function()
+  ["true"] = (function()
     return true
-  end,
+  end),
+  tonumber = (function(self)
+    return tonumber(self)
+  end),
   sep = lpeg.P(sep),
   add_file = function(f)
     return table.insert(file_queue, f)
@@ -161,7 +164,7 @@ run = function()
     end
   end
   nomsu.can_optimize = function(f)
-    if not (args.optimized) then
+    if args.optimization == 0 then
       return false
     end
     if args.compile and input_files[f] then
diff --git a/nomsu.moon b/nomsu.moon
index fe0b777..44bdf65 100755
--- a/nomsu.moon
+++ b/nomsu.moon
@@ -13,10 +13,10 @@ EXIT_SUCCESS, EXIT_FAILURE = 0, 1
 usage = [=[
 Nomsu Compiler
 
-Usage: (nomsu | lua nomsu.lua | moon nomsu.moon) [-V version] [-O] [-v] [-c] [-s] [-t] [-I file] [--help | -h] [--version] [--no-core] [file [nomsu args...]]
+Usage: (nomsu | lua nomsu.lua | moon nomsu.moon) [-V version] [-O optimization level] [-v] [-c] [-s] [-t] [-I file] [--help | -h] [--version] [--no-core] [file [nomsu args...]]
 
 OPTIONS
-    -O Run the compiler in optimized mode (use precompiled .lua versions of Nomsu files, when available).
+    -O <level> Run the compiler with the given optimization level (>0: use precompiled .lua versions of Nomsu files, when available).
     -v Verbose: print compiled lua code.
     -c Compile the input files into a .lua files.
     -e Execute the specified string.
@@ -52,7 +52,7 @@ sep = "\0"
 parser = re.compile([[
     args <- {| (flag %sep)* (({~ file ~} -> add_file) %sep)? {:nomsu_args: {| ({(!%sep .)*} %sep)* |} :} %sep? |} !.
     flag <-
-        {:optimized: ("-O" -> true) :}
+        {:optimization: "-O" (%sep? (([0-9]+) -> tonumber))? :}
       / ("-I" %sep? ({~ file ~} -> add_file))
       / ("-e" %sep? (({} {~ file ~}) -> add_exec_string))
       / ({:check_syntax: ("-s" -> true):})
@@ -66,8 +66,7 @@ parser = re.compile([[
       / {:requested_version: "-V" (%sep? {([0-9.])+})? :}
     file <- ("-" -> "stdin") / {(!%sep .)+}
 ]], {
-    true: -> true
-    sep: lpeg.P(sep)
+    true:(-> true), tonumber:(=>tonumber(@)), sep:lpeg.P(sep)
     add_file: (f)-> table.insert(file_queue, f)
     add_exec_string: (pos, s)->
         name = "command line arg @#{pos}.nom"
@@ -110,7 +109,7 @@ run = ->
             input_files[filename] = true
 
     nomsu.can_optimize = (f)->
-        return false unless args.optimized
+        return false if args.optimization == 0
         return false if args.compile and input_files[f]
         return true