diff --git a/README b/README
index f51638f..293c8ae 100644
--- a/README
+++ b/README
@@ -9,16 +9,20 @@ SYNOPSIS
       my $flow = max_flow($g, "source", "sink");
 
 DESCRIPTION
-    Computes the maximum flow in a graph.
+    Computes the maximum flow in a graph, represented using Jarkko
+    Hietaniemi's Graph.pm module.
 
 FUNCTIONS
-    This module provides the following functions:
+    This module provides the following function:
 
     max_flow($g, $s, $t)
         Computes the maximum flow in the graph $g between vertices $s and $t
-        using the Edmonds-Karp algorithm. $g must be a directed graph where
-        the edge weights indicate the capacity of each edge. $s and $t must
-        be vertices in the graph.
+        using the Edmonds-Karp algorithm. $g must be a Graph.pm object, and
+        must be a directed graph where the edge weights indicate the
+        capacity of each edge. The edge weights must be nonnegative. $s and
+        $t must be vertices in the graph. The graph $g must be connected,
+        and for every vertex v besides $s and $t there must be a path from
+        $s to $t that passes through v.
 
         The return value is a new directed graph which has the same vertices
         and edges as $g, but where the edge weights have been adjusted to