diff --git a/sf-writer/sf_h5_writer.cpp b/sf-writer/sf_h5_writer.cpp
index 2aed9cb..3e2cd2c 100644
--- a/sf-writer/sf_h5_writer.cpp
+++ b/sf-writer/sf_h5_writer.cpp
@@ -71,6 +71,10 @@ int main (int argc, char *argv[])
                     sizeof(ModuleFrame),
                     0);
 
+            if (n_bytes_metadata != sizeof(ModuleFrame)) {
+                throw runtime_error("Unexpected number of bytes in metadata.");
+            }
+
             if (i == 0) {
                 pulse_id = metadata_buffer->pulse_id;
             }
@@ -80,10 +84,6 @@ int main (int argc, char *argv[])
                 cout << " instead of " << pulse_id << endl;
             }
 
-            if (n_bytes_metadata != sizeof(ModuleFrame)) {
-                throw runtime_error("Unexpected number of bytes in metadata.");
-            }
-
             auto n_bytes_image = zmq_recv(
                     sockets[i],
                     image_buffer.get(),