diff --git a/Makefile b/Makefile
index 1398ad5..4485aec 100644
--- a/Makefile
+++ b/Makefile
@@ -1,11 +1,11 @@
 .PHONY: all spec duktape libduktape clean cleanlib
 
-CRYSTAL_BIN  := $(shell which crystal)
-SOURCES 		 := $(shell find src -name '*.cr')
+CRYSTAL_BIN := $(shell which crystal)
+SOURCES := $(shell find src -name '*.cr')
 SPEC_SOURCES := $(shell find spec -name '*.cr')
-CURRENT			 := $(shell pwd)
-EXT					 := $(CURRENT)/src/ext
-OUTPUT			 := $(CURRENT)/.build
+CURRENT := $(shell pwd)
+EXT := $(CURRENT)/src/ext
+OUTPUT := $(CURRENT)/.build
 
 all: duktape
 duktape: $(OUTPUT)/duktape
diff --git a/src/ext/Makefile b/src/ext/Makefile
index 3ad3a32..53d3cf3 100644
--- a/src/ext/Makefile
+++ b/src/ext/Makefile
@@ -1,16 +1,28 @@
 .PHONY: libduktape clean
 
-CURRENT			:= $(shell pwd)
-EXT					:= $(CURRENT)
-PREV				:= $(shell dirname `pwd`])
-OUTPUT			:= $(PREV)/.build
-LIBDIR			:= $(PREV)/.build/lib
-INCLUDEDIR	:= $(PREV)/.build/include
+CURRENT := $(shell pwd)
+EXT := $(CURRENT)
+PREV := $(shell dirname `pwd`])
+OUTPUT := $(PREV)/.build
+LIBDIR := $(PREV)/.build/lib
+INCLUDEDIR := $(PREV)/.build/include
+DUK_OPTS = \
+	-DDUK_OPT_DEEP_C_STACK \
+	-DDUK_OPT_DEBUGGER_SUPPORT \
+	-DDUK_OPT_INTERRUPT_COUNTER \
+	-DDUK_OPT_FASTINT
+CFLAGS = \
+	-Wall \
+	-c \
+	-std=c99 \
+	-Os \
+	-fstrict-aliasing \
+	-fomit-frame-pointer
 
 libduktape: $(OUTPUT)/libduktape.o $(LIBDIR)/libduktape.a $(INCLUDEDIR)/duktape.h
 $(OUTPUT)/libduktape.o: $(EXT)/duktape.c
 	@mkdir -p $(OUTPUT)
-	gcc -o $@ $(EXT)/duktape.c -c -Wall -std=c99 -Os -fstrict-aliasing -fomit-frame-pointer -DDUK_OPT_DEEP_C_STACK -DDUK_OPT_DEBUGGER_SUPPORT -DDUK_OPT_INTERRUPT_COUNTER -DDUK_OPT_FASTINT
+	gcc -o $@ $(EXT)/duktape.c $(CFLAGS) $(DUK_OPTS)
 $(LIBDIR)/libduktape.a:
 	@mkdir -p $(LIBDIR)
 	ar rcs $(LIBDIR)/libduktape.a $(OUTPUT)/libduktape.o
diff --git a/src/lib_duktape.cr b/src/lib_duktape.cr
index cc58976..6a55325 100644
--- a/src/lib_duktape.cr
+++ b/src/lib_duktape.cr
@@ -4,7 +4,7 @@
 #
 # This is free software. Please see LICENSE for details.
 
-@[Link(ldflags: "-L#{__DIR__}/.build/lib -L#{__DIR__}/.build/include -lduktape")]
+@[Link(ldflags: "-L#{__DIR__}/.build/lib -L#{__DIR__}/.build/include -lduktape -lm")]
 lib LibDUK
   alias Context  = Void*