diff --git a/docs/command-line.rst b/docs/command-line.rst
index 476807a..b6c3941 100644
--- a/docs/command-line.rst
+++ b/docs/command-line.rst
@@ -94,6 +94,9 @@ Environment variables
 |                          | that host most tools would probably take that    |
 |                          | first one.                                       |
 +--------------------------+--------------------------------------------------+
+| ``BB_NUMBER_THREADS``    | Environment variables to control the concurrency |
+| ``PARALLEL_MAKE``        |                                                  |
++--------------------------+--------------------------------------------------+
 
 .. |aws_cred| replace:: ``AWS_SHARED_CREDENTIALS_FILE``
 .. |git_cred| replace:: ``GIT_CREDENTIAL_HELPER``
diff --git a/kas-container b/kas-container
index 619c9a2..bc52863 100755
--- a/kas-container
+++ b/kas-container
@@ -466,7 +466,7 @@ if [ -n "${KAS_REPO_REF_DIR}" ]; then
 fi
 
 for var in TERM KAS_DISTRO KAS_MACHINE KAS_TARGET KAS_TASK \
-           KAS_PREMIRRORS; do
+           KAS_PREMIRRORS BB_NUMBER_THREADS PARALLEL_MAKE; do
 	if [ -n "$(eval echo \$${var})" ]; then
 		set -- "$@" -e "${var}=$(eval echo \"\$${var}\")"
 	fi
diff --git a/kas/context.py b/kas/context.py
index 2b768fc..6ca5291 100644
--- a/kas/context.py
+++ b/kas/context.py
@@ -105,7 +105,8 @@ class Context:
                             'No default locales set.', distro_bases)
 
         for key in ['http_proxy', 'https_proxy', 'ftp_proxy', 'no_proxy',
-                    'SSH_AUTH_SOCK']:
+                    'SSH_AUTH_SOCK',
+                    'BB_NUMBER_THREADS', 'PARALLEL_MAKE']:
             val = os.environ.get(key, None)
             if val:
                 self.environ[key] = val