diff --git a/chttp.h b/chttp.h
index 6c5a168..9419184 100644
--- a/chttp.h
+++ b/chttp.h
@@ -764,6 +764,11 @@ int http_create_test_certificate(HTTP_String C, HTTP_String O, HTTP_String CN,
 #define HTTP_CLIENT_CAPACITY (1<<7)
 #endif
 
+// Maximum number of descriptors the client will want
+// to wait on. It's one per connection plus the wakeup
+// self-pipe.
+#define HTTP_CLIENT_POLL_CAPACITY (HTTP_CLIENT_CAPACITY+1)
+
 typedef enum {
     HTTP_CLIENT_CONN_FREE,
     HTTP_CLIENT_CONN_WAIT_LINE,
@@ -922,6 +927,11 @@ void http_free_response(HTTP_Response *response);
 #define HTTP_SERVER_CAPACITY (1<<9)
 #endif
 
+// Maximum number of descriptors the server will want
+// to wait on. It's one per connection plus two for the
+// TCP and TLS listener, plus one for the wakeup self-pipe.
+#define HTTP_SERVER_POLL_CAPACITY (HTTP_SERVER_CAPACITY+3)
+
 typedef enum {
 
     // This struct is unused
diff --git a/src/client.h b/src/client.h
index 21007d3..8aa8c7b 100644
--- a/src/client.h
+++ b/src/client.h
@@ -5,6 +5,11 @@
 #define HTTP_CLIENT_CAPACITY (1<<7)
 #endif
 
+// Maximum number of descriptors the client will want
+// to wait on. It's one per connection plus the wakeup
+// self-pipe.
+#define HTTP_CLIENT_POLL_CAPACITY (HTTP_CLIENT_CAPACITY+1)
+
 typedef enum {
     HTTP_CLIENT_CONN_FREE,
     HTTP_CLIENT_CONN_WAIT_LINE,
diff --git a/src/server.h b/src/server.h
index 80bb1df..c99bfa8 100644
--- a/src/server.h
+++ b/src/server.h
@@ -5,6 +5,11 @@
 #define HTTP_SERVER_CAPACITY (1<<9)
 #endif
 
+// Maximum number of descriptors the server will want
+// to wait on. It's one per connection plus two for the
+// TCP and TLS listener, plus one for the wakeup self-pipe.
+#define HTTP_SERVER_POLL_CAPACITY (HTTP_SERVER_CAPACITY+3)
+
 typedef enum {
 
     // This struct is unused