diff --git a/Makefile b/Makefile
index e2aabb1..c6bc38c 100644
--- a/Makefile
+++ b/Makefile
@@ -19,7 +19,7 @@ all: book
 book: epub html pdf
 
 clean:
-	rm -r $(BUILD)
+  rm -r $(BUILD)
 
 epub: $(BUILD)/epub/$(OUTPUT_FILENAME).epub
 
@@ -28,16 +28,16 @@ html: $(BUILD)/html/$(OUTPUT_FILENAME).html
 pdf: $(BUILD)/pdf/$(OUTPUT_FILENAME).pdf
 
 $(BUILD)/epub/$(OUTPUT_FILENAME).epub: $(MAKEFILE) $(METADATA) $(CHAPTERS) $(CSS_FILE) $(IMAGES) \
-																			 $(COVER_IMAGE)
-	mkdir -p $(BUILD)/epub
-	pandoc $(ARGS) --epub-cover-image=$(COVER_IMAGE) -o $@ $(CHAPTERS)
+                                       $(COVER_IMAGE)
+  mkdir -p $(BUILD)/epub
+  pandoc $(ARGS) --epub-cover-image=$(COVER_IMAGE) -o $@ $(CHAPTERS)
 
 $(BUILD)/html/$(OUTPUT_FILENAME).html: $(MAKEFILE) $(METADATA) $(CHAPTERS) $(CSS_FILE) $(IMAGES)
-	mkdir -p $(BUILD)/html
-	pandoc $(ARGS) --standalone --to=html5 -o $@ $(CHAPTERS)
-	cp -R $(IMAGES_FOLDER)/ $(BUILD)/html/$(IMAGES_FOLDER)/
-	cp $(CSS_FILE) $(BUILD)/html/$(CSS_FILE)
+  mkdir -p $(BUILD)/html
+  pandoc $(ARGS) --standalone --to=html5 -o $@ $(CHAPTERS)
+  cp -R $(IMAGES_FOLDER)/ $(BUILD)/html/$(IMAGES_FOLDER)/
+  cp $(CSS_FILE) $(BUILD)/html/$(CSS_FILE)
 
 $(BUILD)/pdf/$(OUTPUT_FILENAME).pdf: $(MAKEFILE) $(METADATA) $(CHAPTERS) $(CSS_FILE) $(IMAGES)
-	mkdir -p $(BUILD)/pdf
-	pandoc $(ARGS) -V documentclass=$(LATEX_CLASS) -o $@ $(CHAPTERS)
+  mkdir -p $(BUILD)/pdf
+  pandoc $(ARGS) -V documentclass=$(LATEX_CLASS) -o $@ $(CHAPTERS)