diff --git a/CMakeLists.txt b/CMakeLists.txt
index 191d1b6ed..0ecd4b65e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -174,6 +174,8 @@ aws_check_headers(${PROJECT_NAME} ${AWS_IO_HEADERS})
 
 aws_add_sanitizers(${PROJECT_NAME})
 
+target_compile_definitions(${PROJECT_NAME} PRIVATE "-DDEBUG_BUILD")
+
 # We are not ABI stable yet
 set_target_properties(${PROJECT_NAME} PROPERTIES VERSION 1.0.0)
 
diff --git a/source/channel.c b/source/channel.c
index eb4e6f0ef..622bf42dc 100644
--- a/source/channel.c
+++ b/source/channel.c
@@ -1005,6 +1005,7 @@ int aws_channel_slot_on_handler_shutdown_complete(
 }
 
 size_t aws_channel_slot_downstream_read_window(struct aws_channel_slot *slot) {
+    AWS_FATAL_ASSERT(false);
     AWS_ASSERT(slot->adj_right);
     return slot->channel->read_back_pressure_enabled ? slot->adj_right->window_size : SIZE_MAX;
 }
diff --git a/source/channel_bootstrap.c b/source/channel_bootstrap.c
index 63cc3484e..e60105040 100644
--- a/source/channel_bootstrap.c
+++ b/source/channel_bootstrap.c
@@ -1583,6 +1583,8 @@ static void s_on_server_channel_on_setup_completed(struct aws_channel *channel,
              * when a TLS connection has been successfully established. At that point, we signal a successful TLS
              * handshake, which also makes the server name and protocol available (if provided).
              */
+            // FIXME A code path used in the tls_server_hangup_during_negotiation test needs a slot
+            //   set by s_setup_server_tls.
             s_tls_server_on_negotiation_result(socket_channel_handler, socket_slot, err_code, channel_data);
             return;
         }
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 571b5d42a..15bebbcc6 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -423,6 +423,7 @@ generate_test_driver(${TEST_BINARY_NAME})
 if(USE_S2N)
     target_compile_definitions(${PROJECT_NAME}-tests PRIVATE "-DUSE_S2N")
 endif()
+target_compile_definitions(${PROJECT_NAME}-tests PRIVATE "-DDEBUG_BUILD")
 
 # SSL certificates to use for testing.
 add_custom_command(TARGET ${TEST_BINARY_NAME} PRE_BUILD