diff --git a/functional-tests/scenario-string-constants.scm b/functional-tests/scenario-string-constants.scm
index e416ed0..88c9ab9 100644
--- a/functional-tests/scenario-string-constants.scm
+++ b/functional-tests/scenario-string-constants.scm
@@ -75,20 +75,34 @@ Options:
   {-V|--version}")
 
   (define thin-metadata-pack-help
-    "Usage: thin_metadata_pack [options]
-Options:
-  {-i|--input} <input metadata (binary format)>
-  {-o|--output} <output packed metadata>
-  {-h|--help}
-  {-V|--version}")
+    "thin_metadata_pack 0.8.5
+Produces a compressed file of thin metadata.  Only packs metadata blocks that are actually used.
+
+USAGE:
+    thin_metadata_pack -i <DEV> -o <FILE>
+
+FLAGS:
+    -h, --help       Prints help information
+    -V, --version    Prints version information
+
+OPTIONS:
+    -i <DEV>         Specify thinp metadata binary device/file
+    -o <FILE>        Specify packed output file")
 
   (define thin-metadata-unpack-help
-    "Usage: thin_metadata_unpack [options]
-Options:
-  {-i|--input} <input packed metadata>
-  {-o|--output} <output metadata (binary format)>
-  {-h|--help}
-  {-V|--version}")
+    "thin_metadata_unpack 0.8.5
+Unpack a compressed file of thin metadata.
+
+USAGE:
+    thin_metadata_unpack -i <DEV> -o <FILE>
+
+FLAGS:
+    -h, --help       Prints help information
+    -V, --version    Prints version information
+
+OPTIONS:
+    -i <DEV>         Specify thinp metadata binary device/file
+    -o <FILE>        Specify packed output file")
 
   (define cache-check-help
     "Usage: cache_check [options] {device|file}
diff --git a/functional-tests/thin-functional-tests.scm b/functional-tests/thin-functional-tests.scm
index 0537642..b6e5a77 100644
--- a/functional-tests/thin-functional-tests.scm
+++ b/functional-tests/thin-functional-tests.scm
@@ -509,17 +509,17 @@
   ;;;-----------------------------------------------------------
 
   (define-scenario (thin-metadata-pack version)
-    "thin_metadata_pack accepts --version"
+    "accepts --version"
     (run-ok-rcv (stdout _) (thin-metadata-pack "--version")
-      (assert-equal tools-version stdout)))
+      (assert-equal "thin_metadata_pack 0.8.5" stdout)))
 
   (define-scenario (thin-metadata-pack h)
-    "thin_metadata_pack accepts -h"
+    "accepts -h"
     (run-ok-rcv (stdout _) (thin-metadata-pack "-h")
       (assert-equal thin-metadata-pack-help stdout)))
 
   (define-scenario (thin-metadata-pack help)
-    "thin_metadata_pack accepts --help"
+    "accepts --help"
     (run-ok-rcv (stdout _) (thin-metadata-pack "--help")
       (assert-equal thin-metadata-pack-help stdout)))
 
@@ -527,41 +527,41 @@
     "Unrecognised option should cause failure"
     (with-valid-metadata (md)
       (run-fail-rcv (stdout stderr) (thin-metadata-pack "--unleash-the-hedgehogs")
-        (assert-matches ".*thin_metadata_pack: unrecognized option '--unleash-the-hedgehogs" stderr))))
+        (assert-starts-with "error: Found argument '--unleash-the-hedgehogs'" stderr)))) 
 
   (define-scenario (thin-metadata-pack missing-input-file)
     "the input file wasn't specified"
     (with-empty-metadata (md)
       (run-fail-rcv (_ stderr) (thin-metadata-pack "-o " md)
-        (assert-starts-with "No input file provided." stderr))))
+        (assert-starts-with "error: The following required arguments were not provided:\n    -i <DEV>" stderr))))
 
   (define-scenario (thin-metadata-pack no-such-input-file)
     "the input file can't be found"
     (with-empty-metadata (md)
       (run-fail-rcv (_ stderr) (thin-metadata-pack "-i no-such-file -o" md)
-        (assert-starts-with "Couldn't stat path" stderr))))
+        (assert-starts-with "Couldn't find input file" stderr))))
 
   (define-scenario (thin-metadata-pack missing-output-file)
     "the output file wasn't specified"
     (with-empty-metadata (md)
       (run-fail-rcv (_ stderr) (thin-metadata-pack "-i" md)
-        (assert-starts-with "No output file provided." stderr))))
+        (assert-starts-with "error: The following required arguments were not provided:\n    -o <FILE>" stderr))))
 
   ;;;-----------------------------------------------------------
-  ;;; thin_metadata_pack scenarios
+  ;;; thin_metadata_unpack scenarios
   ;;;-----------------------------------------------------------
   (define-scenario (thin-metadata-unpack version)
-    "thin_metadata_pack accepts --version"
+    "accepts --version"
     (run-ok-rcv (stdout _) (thin-metadata-unpack "--version")
-      (assert-equal tools-version stdout)))
+      (assert-equal "thin_metadata_unpack 0.8.5" stdout)))
 
   (define-scenario (thin-metadata-unpack h)
-    "thin_metadata_pack accepts -h"
+    "accepts -h"
     (run-ok-rcv (stdout _) (thin-metadata-unpack "-h")
       (assert-equal thin-metadata-unpack-help stdout)))
 
   (define-scenario (thin-metadata-unpack help)
-    "thin_metadata_pack accepts --help"
+    "accepts --help"
     (run-ok-rcv (stdout _) (thin-metadata-unpack "--help")
       (assert-equal thin-metadata-unpack-help stdout)))
 
@@ -569,25 +569,25 @@
     "Unrecognised option should cause failure"
     (with-valid-metadata (md)
       (run-fail-rcv (stdout stderr) (thin-metadata-unpack "--unleash-the-hedgehogs")
-        (assert-matches ".*thin_metadata_unpack: unrecognized option '--unleash-the-hedgehogs" stderr))))
+        (assert-starts-with "error: Found argument '--unleash-the-hedgehogs'" stderr)))) 
 
   (define-scenario (thin-metadata-unpack missing-input-file)
     "the input file wasn't specified"
     (with-empty-metadata (md)
       (run-fail-rcv (_ stderr) (thin-metadata-unpack "-o " md)
-        (assert-starts-with "No input file provided." stderr))))
+        (assert-starts-with "error: The following required arguments were not provided:\n    -i <DEV>" stderr))))
 
   (define-scenario (thin-metadata-unpack no-such-input-file)
     "the input file can't be found"
     (with-empty-metadata (md)
       (run-fail-rcv (_ stderr) (thin-metadata-unpack "-i no-such-file -o" md)
-        (assert-starts-with "Couldn't open pack file" stderr))))
+        (assert-starts-with "Couldn't find input file" stderr))))
 
   (define-scenario (thin-metadata-unpack missing-output-file)
     "the output file wasn't specified"
     (with-empty-metadata (md)
       (run-fail-rcv (_ stderr) (thin-metadata-unpack "-i" md)
-        (assert-starts-with "No output file provided." stderr))))
+        (assert-starts-with "error: The following required arguments were not provided:\n    -o <FILE>" stderr))))
 
   (define-scenario (thin-metadata-unpack garbage-input-file)
     "the input file is just zeroes"
diff --git a/src/bin/thin_metadata_pack.rs b/src/bin/thin_metadata_pack.rs
index 27d0435..6019147 100644
--- a/src/bin/thin_metadata_pack.rs
+++ b/src/bin/thin_metadata_pack.rs
@@ -2,7 +2,8 @@ extern crate clap;
 extern crate thinp;
 
 use clap::{App, Arg};
-use std::process;
+use std::process::exit;
+use thinp::file_utils;
 
 fn main() {
     let parser = App::new("thin_metadata_pack")
@@ -25,8 +26,13 @@ fn main() {
     let input_file = matches.value_of("INPUT").unwrap();
     let output_file = matches.value_of("OUTPUT").unwrap();
 
+    if !file_utils::file_exists(input_file) {
+        eprintln!("Couldn't find input file '{}'.", &input_file);
+        exit(1);
+    }
+    
     if let Err(reason) = thinp::pack::pack::pack(&input_file, &output_file) {
         println!("Application error: {}\n", reason);
-        process::exit(1);
+        exit(1);
     }
 }
diff --git a/src/bin/thin_metadata_unpack.rs b/src/bin/thin_metadata_unpack.rs
index 1a7436d..79cdd87 100644
--- a/src/bin/thin_metadata_unpack.rs
+++ b/src/bin/thin_metadata_unpack.rs
@@ -3,6 +3,9 @@ extern crate thinp;
 
 use clap::{App, Arg};
 use std::process;
+use thinp::file_utils;
+
+use std::process::exit;
 
 fn main() {
     let parser = App::new("thin_metadata_unpack")
@@ -21,11 +24,15 @@ fn main() {
             .value_name("FILE")
             .takes_value(true));
 
-
     let matches = parser.get_matches();
     let input_file = matches.value_of("INPUT").unwrap();
     let output_file = matches.value_of("OUTPUT").unwrap();
 
+    if !file_utils::file_exists(input_file) {
+        eprintln!("Couldn't find input file '{}'.", &input_file);
+        exit(1);
+    }
+    
     if let Err(reason) = thinp::pack::pack::unpack(&input_file, &output_file) {
         println!("Application error: {}", reason);
         process::exit(1);
diff --git a/src/lib.rs b/src/lib.rs
index b51595b..9a193e1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,5 +13,6 @@ extern crate quickcheck_macros;
 
 pub mod block_manager;
 pub mod check;
+pub mod file_utils;
 pub mod pack;
 pub mod version;
diff --git a/src/pack/pack.rs b/src/pack/pack.rs
index 3406372..b4afa15 100644
--- a/src/pack/pack.rs
+++ b/src/pack/pack.rs
@@ -168,12 +168,26 @@ fn read_header<R>(mut r: R) -> io::Result<u64>
 where
     R: byteorder::ReadBytesExt,
 {
+    use std::process::exit;
+    
     let magic = r.read_u64::<LittleEndian>()?;
-    assert_eq!(magic, MAGIC);
+    if magic != MAGIC {
+        eprintln!("Not a pack file.");
+        exit(1);
+    }
+    
     let version = r.read_u64::<LittleEndian>()?;
-    assert_eq!(version, PACK_VERSION);
+    if version != PACK_VERSION {
+        eprintln!("unsupported pack file version ({}).", PACK_VERSION);
+        exit(1);
+    }
+    
     let block_size = r.read_u64::<LittleEndian>()?;
-    assert_eq!(block_size, 4096);
+    if block_size != BLOCK_SIZE {
+        eprintln!("block size is not {}", BLOCK_SIZE);
+        exit(1);
+    }
+
     r.read_u64::<LittleEndian>()
 }