diff --git a/.gitignore b/.gitignore
deleted file mode 100644
index 1369984..0000000
--- a/.gitignore
+++ /dev/null
@@ -1,2 +0,0 @@
-/makefile.csm
-/rain
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..11f1fc7
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,19 @@
+CSM := csm
+PREFIX := /usr/local
+INSTALL := install
+
+.PHONY: all
+all: Makefile.csm
+	$(MAKE) -f Makefile.csm
+
+Makefile.csm:
+	$(CSM) -makefile Makefile.csm
+
+.PHONY: clean
+clean: Makefile.csm
+	$(MAKE) -f Makefile.csm clean
+	rm -f Makefile.csm rain
+
+.PHONY: install
+install:
+	$(INSTALL) -sDm755 rain $(DESTDIR)$(PREFIX)/bin/rain
diff --git a/README.md b/README.md
index 6b504a3..d7538b6 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 # Dependencies
 
 - [CHICKEN Scheme](https://call-cc.org) 5 or 6;
-- A few CHICKEN extensions, installable using `chicken-install -s format html-parser openssl http-client matchable`.
+- A few CHICKEN extensions, installable using `chicken-install -s html-parser openssl http-client matchable srfi-18`.
 
 # Building
 
diff --git a/makefile b/makefile
deleted file mode 100644
index 738144f..0000000
--- a/makefile
+++ /dev/null
@@ -1,18 +0,0 @@
-CSM := csm
-PREFIX := /usr/local
-INSTALL := install
-
-.PHONY: all
-all: makefile.csm
-	$(MAKE) -f makefile.csm
-
-makefile.csm:
-	$(CSM) -makefile makefile.csm
-
-.PHONY: clean
-clean:
-	git clean -fdx
-
-.PHONY: install
-install:
-	$(INSTALL) -sDm755 rain $(DESTDIR)$(PREFIX)/bin/rain
diff --git a/rain.scm b/rain.scm
index 7440640..b3e8b7e 100644
--- a/rain.scm
+++ b/rain.scm
@@ -1,3 +1,5 @@
+(define parallel 1)
+
 (define (find-comic-image index)
   (call-with-current-continuation
    (lambda (k)
@@ -9,7 +11,7 @@
 
 (define (download-comic-image index)
   (format (current-error-port) "* downloading comic image ~a~%" index)
-  (call-with-output-file (format #f "rain-~4,48,d.png" (string->number index))
+  (call-with-output-file (format #f "rain-~a.png" index)
     (lambda (out)
       (call-with-input-request (find-comic-image index)
                                #f
@@ -18,20 +20,38 @@
   (format (current-error-port) "* downloaded comic image ~a~%" index))
 
 (define (download-all indices)
-  (for-each download-comic-image indices))
+  (format (current-error-port) "* using ~a threads~%" parallel)
+  (for-each download-batch (chop indices parallel)))
+
+(define (download-batch batch)
+  (let ((threads (map (lambda (index)
+                        (make-thread
+                         (lambda ()
+                           (download-comic-image index))))
+                      batch)))
+    (for-each thread-start! threads)
+    (for-each thread-join! threads)))
 
 (define (usage)
   (format (current-error-port) "usage: ~a [OPTION ...] INDEX ...~%" (program-name))
   (format (current-error-port) "options:~%")
   (format (current-error-port) "  -h|-help        display this help message~%")
-  (format (current-error-port) "  -v|-version     display version information~%"))
+  (format (current-error-port) "  -v|-version     display version information~%")
+  (format (current-error-port) "  -j|-parallel N  download N images in parallel~%"))
 
 (define parse-command-line
   (match-lambda
     (((or "-h" "-help") . _)
      (usage))
     (((or "-v" "-version") . _)
-     (format (current-error-port) "rain.scm 1.0.1~%" (program-name)))
+     (format (current-error-port) "rain.scm 1.0.0~%" (program-name)))
+    (((or "-j" "-parallel") n . rest)
+     (let ((nn (string->number n)))
+       (unless nn
+         (usage)
+         (exit 1))
+       (set! parallel nn)
+       (parse-command-line rest)))
     (()
      (usage))
     (indices
diff --git a/rain.sld b/rain.sld
index 12d74bb..0c2c22e 100755
--- a/rain.sld
+++ b/rain.sld
@@ -8,12 +8,13 @@ exec csi -s "$0" "$@"
    (scheme file)
    (chicken base)
    (chicken io)
+   (chicken format)
    (chicken port)
    (chicken process-context)
-   (format)
    (html-parser)
    (openssl)                            ; has to be before http-client
    (http-client)
-   (matchable))
+   (matchable)
+   (srfi-18))
   (include "rain.scm")
   (begin (main (command-line-arguments))))