diff --git a/main.c b/main.c
index da1608e..654c12b 100644
--- a/main.c
+++ b/main.c
@@ -540,16 +540,7 @@ int main(int argc, char *argv[])
 		control->flags &= ~FLAG_UNLIMITED;
 	}
 
-	/* Work out the compression overhead per compression thread for the
-	 * compression back-ends that need a lot of ram */
-	if (LZMA_COMPRESS) {
-		int level = control->compression_level * 7 / 9 ? : 1;
-		i64 dictsize = (level <= 5 ? (1 << (level * 2 + 14)) :
-				(level == 6 ? (1 << 25) : (1 << 26)));
-
-		control->overhead = (dictsize * 23 / 2) + (4 * 1024 * 1024);
-	} else if (ZPAQ_COMPRESS)
-		control->overhead = 112 * 1024 * 1024;
+	setup_overhead(control);
 
 	/* Set the main nice value to half that of the backend threads since
 	 * the rzip stage is usually the rate limiting step */
diff --git a/util.c b/util.c
index 930a37f..a92fa7e 100644
--- a/util.c
+++ b/util.c
@@ -133,6 +133,20 @@ void failure(const char *format, ...)
 	fatal_exit();
 }
 
+void setup_overhead(rzip_control *control)
+{
+	/* Work out the compression overhead per compression thread for the
+	 * compression back-ends that need a lot of ram */
+	if (LZMA_COMPRESS) {
+		int level = control->compression_level * 7 / 9 ? : 1;
+		i64 dictsize = (level <= 5 ? (1 << (level * 2 + 14)) :
+				(level == 6 ? (1 << 25) : (1 << 26)));
+
+		control->overhead = (dictsize * 23 / 2) + (4 * 1024 * 1024);
+	} else if (ZPAQ_COMPRESS)
+		control->overhead = 112 * 1024 * 1024;
+}
+
 void setup_ram(rzip_control *control)
 {
 	/* Use less ram when using STDOUT to store the temporary output file. */
diff --git a/util.h b/util.h
index 8b8bf90..d70a7a9 100644
--- a/util.h
+++ b/util.h
@@ -27,6 +27,7 @@ void unlink_files(void);
 void register_outputfile(FILE *f);
 void fatal(const char *format, ...);
 void failure(const char *format, ...);
+void setup_overhead(rzip_control *control);
 void setup_ram(rzip_control *control);
 void round_to_page(i64 *size);
 void get_rand(uchar *buf, int len);