diff --git a/doc/d-utils.md b/doc/d-utils.md
new file mode 100644
index 0000000..99d2ad9
--- /dev/null
+++ b/doc/d-utils.md
@@ -0,0 +1,17 @@
+# Utility modules
+
+## util-time [module]
+
+Compatibility time module for <5.2 and >=5.3 versions of CHICKEN.
+
+### current-util-milliseconds [procedure]
+
+    (current-util-milliseconds)
+
+Returns the current milliseconds counter that can be used for high-precision time measurements.
+
+### seconds->iso-date-string [procedure]
+
+    (seconds->iso-date-string . args)
+
+Converts given seconds to ISO date string. Defaults to ```(current-seconds)```.
diff --git a/src/Makefile b/src/Makefile
index a5f5461..4e79587 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -289,7 +289,8 @@ UTIL-IO-SOURCES=util-io.scm
 util-io.o: util-io.import.scm
 util-io.import.scm: $(UTIL-IO-SOURCES)
 
-UTIL-STRING-SOURCES=util-string.scm testing.import.scm util-utf8.scm
+UTIL-STRING-SOURCES=util-string.scm testing.import.scm	\
+	util-utf8.import.scm
 
 util-string.o: util-string.import.scm
 util-string.import.scm: $(UTIL-STRING-SOURCES)
diff --git a/src/gendoc.scm b/src/gendoc.scm
index 5ea08b8..f364c86 100644
--- a/src/gendoc.scm
+++ b/src/gendoc.scm
@@ -1,7 +1,20 @@
 
-(import duck-extract
-	util-time)
+(import duck-extract)
 
-(print "# Utility modules")
-(newline)
-(print-module-duck util-time)
+(define-syntax gen-duck
+  (syntax-rules ()
+    ((_ fname title mod ...)
+     (begin
+       (import mod ...)
+       (with-output-to-file fname
+	 (lambda ()
+	   (print "# " title)
+	   (let ()
+	     (newline)
+	     (print-module-duck mod))
+	   ...
+	   ))))))
+
+(gen-duck "doc/d-utils.md"
+	  "Utility modules"
+	  util-time)