diff --git a/Makefile.in b/Makefile.in
index 14da10f..4264191 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -25,6 +25,7 @@ PROGRAMS=\
 all: $(PROGRAMS)
 
 SOURCE=\
+	base/output_file_requirements.cc \
 	base/application.cc \
 	base/base64.cc \
 	base/disk_units.cc \
diff --git a/base/application.cc b/base/application.cc
index 0ec1749..3c5202c 100644
--- a/base/application.cc
+++ b/base/application.cc
@@ -61,8 +61,14 @@ application::run(int argc, char **argv)
 
 	std::list<command::ptr>::const_iterator it;
 	for (it = cmds_.begin(); it != cmds_.end(); ++it) {
-		if (cmd == (*it)->get_name())
-			return (*it)->run(argc, argv);
+		if (cmd == (*it)->get_name()) {
+			try {
+				return (*it)->run(argc, argv);
+			} catch (std::exception const &e) {
+				cerr << e.what() << "\n";
+				return 1;
+			}
+		}
 	}
 
 	std::cerr << "Unknown command '" << cmd << "'\n";
diff --git a/base/output_file_requirements.cc b/base/output_file_requirements.cc
new file mode 100644
index 0000000..001e127
--- /dev/null
+++ b/base/output_file_requirements.cc
@@ -0,0 +1,51 @@
+#include "base/output_file_requirements.h"
+
+#include <iostream>
+#include <linux/fs.h>
+#include <sstream>
+#include <stdexcept>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+using namespace base;
+using namespace std;
+
+//----------------------------------------------------------------
+
+namespace {
+	void explain_output_file_requirements() {
+		ostringstream out;
+		out << "The output file should either be a block device,\n"
+		    << "or an existing file.  The file needs to be large\n"
+		    << "enough to hold the metadata.";
+
+		throw runtime_error(out.str());
+	}
+
+	unsigned const MIN_SIZE = 32 * 1024;
+}
+
+void
+base::check_output_file_requirements(string const &path)
+{
+	struct stat info;
+	int r = ::stat(path.c_str(), &info);
+	if (r) {
+		cerr << "Output file does not exist.\n\n";
+		explain_output_file_requirements();
+	}
+
+	if (!info.st_size) {
+		cerr << "Zero size output file.\n\n";
+		explain_output_file_requirements();
+	}
+
+	if (info.st_size < MIN_SIZE) {
+		cerr << "Output file too small.\n\n";
+		explain_output_file_requirements();
+	}
+}
+
+//----------------------------------------------------------------
diff --git a/base/output_file_requirements.h b/base/output_file_requirements.h
new file mode 100644
index 0000000..5d1f85f
--- /dev/null
+++ b/base/output_file_requirements.h
@@ -0,0 +1,14 @@
+#ifndef BASE_OUTPUT_FILE_REQUIREMENTS_H
+#define BASE_OUTPUT_FILE_REQUIREMENTS_H
+
+#include <string>
+
+//----------------------------------------------------------------
+
+namespace base {
+	void check_output_file_requirements(std::string const &path);
+}
+
+//----------------------------------------------------------------
+
+#endif
diff --git a/caching/cache_repair.cc b/caching/cache_repair.cc
index dfe644b..bfc92c8 100644
--- a/caching/cache_repair.cc
+++ b/caching/cache_repair.cc
@@ -2,6 +2,7 @@
 #include <getopt.h>
 #include <libgen.h>
 
+#include "base/output_file_requirements.h"
 #include "caching/commands.h"
 #include "caching/metadata.h"
 #include "caching/metadata_dump.h"
@@ -105,7 +106,10 @@ cache_repair_cmd::run(int argc, char **argv)
 		return 1;
 	}
 
-	if (!output_path) {
+	if (output_path)
+		check_output_file_requirements(*output_path);
+
+	else {
 		cerr << "no output file provided" << endl;
 		usage(cerr);
 		return 1;
diff --git a/caching/cache_restore.cc b/caching/cache_restore.cc
index a357eed..efa8e98 100644
--- a/caching/cache_restore.cc
+++ b/caching/cache_restore.cc
@@ -1,5 +1,6 @@
 #include "version.h"
 
+#include "base/output_file_requirements.h"
 #include "caching/commands.h"
 #include "caching/metadata.h"
 #include "caching/restore_emitter.h"
@@ -169,7 +170,10 @@ cache_restore_cmd::run(int argc, char **argv)
 		return 1;
 	}
 
-	if (!fs.output) {
+	if (fs.output)
+		check_output_file_requirements(*fs.output);
+
+	else {
 		cerr << "No output file provided." << endl << endl;
 		usage(cerr);
 		return 1;
diff --git a/era/era_restore.cc b/era/era_restore.cc
index 0f41a96..97dff35 100644
--- a/era/era_restore.cc
+++ b/era/era_restore.cc
@@ -1,5 +1,6 @@
 #include "version.h"
 
+#include "base/output_file_requirements.h"
 #include "era/commands.h"
 #include "era/metadata.h"
 #include "era/restore_emitter.h"
@@ -121,7 +122,10 @@ era_restore_cmd::run(int argc, char **argv)
 		return 1;
 	}
 
-	if (!fs.output) {
+	if (fs.output)
+		check_output_file_requirements(*fs.output);
+
+	else {
 		cerr << "No output file provided." << endl << endl;
 		usage(cerr);
 		return 1;
diff --git a/features/step_definitions/thin_steps.rb b/features/step_definitions/thin_steps.rb
index 1900293..39527f4 100644
--- a/features/step_definitions/thin_steps.rb
+++ b/features/step_definitions/thin_steps.rb
@@ -24,6 +24,11 @@ Given(/^a corrupt superblock$/) do
   end
 end
 
+Given(/^a tiny file$/) do
+  run_simple("rm -f tiny")
+  run_simple("fallocate -l 123 tiny")
+end
+
 When(/^I run thin_check with (.*?)$/) do |opts|
   run_simple("thin_check #{opts} #{dev_file}", false)
 end
diff --git a/features/thin_restore.feature b/features/thin_restore.feature
index e5bdb04..1c1a7f4 100644
--- a/features/thin_restore.feature
+++ b/features/thin_restore.feature
@@ -55,6 +55,18 @@ Feature: thin_restore
     No output file provided.
     """
 
+  Scenario: tiny output file
+    Given a tiny file
+    When I run thin_restore with -i metadata.xml -o tiny
+    Then it should fail with:
+    """
+    Output file too small.
+
+    The output file should either be a block device,
+    or an existing file.  The file needs to be large
+    enough to hold the metadata.
+    """
+
   Scenario: --quiet is accepted
     Given valid thin metadata
     When I run thin_restore with -i metadata.xml -o metadata.bin --quiet
diff --git a/man8/cache_repair.8 b/man8/cache_repair.8
index b702707..f701e77 100644
--- a/man8/cache_repair.8
+++ b/man8/cache_repair.8
@@ -32,7 +32,8 @@ This tool cannot be run on live metadata.
 Input file or device with binary metadata.
 
 .IP "\fB\-o, \-\-output\fP \fI{device|file}\fP"
-Output file or device for repaired binary metadata.
+Output file or device for repaired binary metadata.  If a file is used
+then it must be preallocated, and large enough to hold the metadata.
 
 .IP "\fB\-h, \-\-help\fP"
 Print help and exit.
diff --git a/man8/cache_restore.8 b/man8/cache_restore.8
index d9fd580..9a1de2f 100644
--- a/man8/cache_restore.8
+++ b/man8/cache_restore.8
@@ -30,7 +30,8 @@ This tool cannot be run on live metadata.
 Input file or device with metadata.
 
 .IP "\fB\-o, \-\-output\fP \fI{device|file}\fP"
-Output file or device.
+Output file or device for repaired binary metadata.  If a file is used
+then it must be preallocated, and large enough to hold the metadata.
 
 .IP "\fB{\-\-debug-override-metadata-version}\fP \fI<integer>\fP"
 ONLY FOR DEBUGGING PURPOSES:
diff --git a/man8/thin_repair.8 b/man8/thin_repair.8
index a8bd529..8e063fc 100644
--- a/man8/thin_repair.8
+++ b/man8/thin_repair.8
@@ -32,7 +32,8 @@ This tool cannot be run on live metadata.
 Input file or device with binary metadata.
 
 .IP "\fB\-o, \-\-output\fP \fI{device|file}\fP"
-Output file or device for repaired binary metadata.
+Output file or device for repaired binary metadata.  If a file is used
+then it must be preallocated, and large enough to hold the metadata.
 
 .IP "\fB\-h, \-\-help\fP"
 Print help and exit.
diff --git a/man8/thin_restore.8 b/man8/thin_restore.8
index f4d590d..02dd33c 100644
--- a/man8/thin_restore.8
+++ b/man8/thin_restore.8
@@ -33,7 +33,8 @@ Suppress output messages, return only exit code.
 Input file or device with metadata.
 
 .IP "\fB\-o, \-\-output\fP \fI{device|file}\fP"
-Output file or device.
+Output file or device for repaired binary metadata.  If a file is used
+then it must be preallocated, and large enough to hold the metadata.
 
 .IP "\fB\-h, \-\-help\fP"
 Print help and exit.
diff --git a/persistent-data/file_utils.cc b/persistent-data/file_utils.cc
index 4ed190e..4fd513d 100644
--- a/persistent-data/file_utils.cc
+++ b/persistent-data/file_utils.cc
@@ -22,8 +22,11 @@ persistent_data::get_nr_blocks(string const &path, block_address block_size)
 	block_address nr_blocks;
 
 	int r = ::stat(path.c_str(), &info);
-	if (r)
-		throw runtime_error("Couldn't stat dev path");
+	if (r) {
+		ostringstream out;
+		out << "Couldn't stat dev path '" << path << "'";
+		throw runtime_error(out.str());
+	}
 
 	if (S_ISREG(info.st_mode) && info.st_size)
 		nr_blocks = div_down<block_address>(info.st_size, block_size);
diff --git a/thin-provisioning/thin_repair.cc b/thin-provisioning/thin_repair.cc
index 2741b78..716970e 100644
--- a/thin-provisioning/thin_repair.cc
+++ b/thin-provisioning/thin_repair.cc
@@ -2,6 +2,7 @@
 #include <getopt.h>
 #include <libgen.h>
 
+#include "base/output_file_requirements.h"
 #include "persistent-data/file_utils.h"
 #include "thin-provisioning/commands.h"
 #include "human_readable_format.h"
@@ -99,7 +100,10 @@ thin_repair_cmd::run(int argc, char **argv)
 		return 1;
 	}
 
-	if (!output_path) {
+	if (output_path)
+		check_output_file_requirements(*output_path);
+
+	else {
 		cerr << "no output file provided" << endl;
 		usage(cerr);
 		return 1;
diff --git a/thin-provisioning/thin_restore.cc b/thin-provisioning/thin_restore.cc
index b779b94..6c23c04 100644
--- a/thin-provisioning/thin_restore.cc
+++ b/thin-provisioning/thin_restore.cc
@@ -16,6 +16,7 @@
 // with thin-provisioning-tools.  If not, see
 // <http://www.gnu.org/licenses/>.
 
+#include "base/output_file_requirements.h"
 #include "persistent-data/file_utils.h"
 #include "thin-provisioning/commands.h"
 #include "thin-provisioning/emitter.h"
@@ -138,7 +139,8 @@ thin_restore_cmd::run(int argc, char **argv)
 		cerr << "No output file provided." << endl << endl;
 		usage(cerr);
 		return 1;
-	}
+	} else
+		check_output_file_requirements(output);
 
 	return restore(input, output, quiet);
 }