diff --git a/conda_smithy/configure_feedstock.py b/conda_smithy/configure_feedstock.py
index 3ce69495a..ee4d8ef78 100755
--- a/conda_smithy/configure_feedstock.py
+++ b/conda_smithy/configure_feedstock.py
@@ -178,9 +178,7 @@ def render_circle(jinja_env, forge_config, forge_dir):
             forge_config['upload_script'] = "upload_or_check_non_existence"
 
         # TODO: Conda has a convenience for accessing nested yaml content.
-        templates = forge_config.get('templates', {})
-        template_name = templates.get('run_docker_build',
-                                      'run_docker_build_matrix.tmpl')
+        template_name = 'run_docker_build.tmpl'
         template = jinja_env.get_template(template_name)
         target_fname = os.path.join(forge_dir, 'ci_support', 'run_docker_build.sh')
         with write_file(target_fname) as fh:
@@ -650,7 +648,7 @@ def main(forge_file_directory):
     config = {'docker': {'executable': 'docker',
                          'image': 'condaforge/linux-anvil',
                          'command': 'bash'},
-              'templates': {'run_docker_build': 'run_docker_build_matrix.tmpl'},
+              'templates': {},
               'travis': {},
               'circle': {},
               'appveyor': {},
@@ -702,7 +700,8 @@ def main(forge_file_directory):
 
     tmplt_dir = os.path.join(conda_forge_content, 'templates')
     # Load templates from the feedstock in preference to the smithy's templates.
-    env = Environment(loader=FileSystemLoader([os.path.join(forge_dir, 'templates'),
+    env = Environment(extensions=['jinja2.ext.do'],
+                      loader=FileSystemLoader([os.path.join(forge_dir, 'templates'),
                                                tmplt_dir]))
 
     copy_feedstock_content(forge_dir)
diff --git a/conda_smithy/templates/circle.yml.tmpl b/conda_smithy/templates/circle.yml.tmpl
index 5c5be5688..e9b82d481 100644
--- a/conda_smithy/templates/circle.yml.tmpl
+++ b/conda_smithy/templates/circle.yml.tmpl
@@ -1,3 +1,10 @@
+{%- macro matrix_case_name(matrix_item) -%}
+    build
+    {%- for dep, ver in matrix_item -%}
+        __{{ dep }}_{{ ver }}
+    {%- endfor %}
+{%- endmacro -%}
+
 version: 2
 
 jobs:
@@ -14,9 +21,16 @@ jobs:
           # The Circle-CI build should not be active, but if this is not true for some reason, do a fast finish.
           command: exit 0
 {%- else %}
-  build:
+{%- for case in matrix %}
+  {{ matrix_case_name(case) }}:
     working_directory: ~/test
     machine: true
+    {%- if case[0] %}
+    environment:
+      {%- for dep, ver in case %}
+      - {{ dep }}: "{{ ver }}"
+      {%- endfor -%}
+    {%- endif %}
     steps:
       - checkout
       - run:
@@ -26,9 +40,18 @@ jobs:
             ./ci_support/checkout_merge_commit.sh
       - run:
           command: docker pull condaforge/linux-anvil
+      {%- if case[0] %}
+      - run:
+          name: Print conda-build environment variables
+          command: |
+            {%- for dep, ver in case %}
+            echo {{ '"' }}{{ dep }}{{ '=${' }}{{ dep }}{{ '}"' }}
+            {%- endfor -%}
+      {%- endif %}
       - run:
           # Run, test and (if we have a BINSTAR_TOKEN) upload the distributions.
           command: ./ci_support/run_docker_build.sh
+{%- endfor -%}
 {%- endif -%}
 {%- endblock %}
 
@@ -44,7 +67,9 @@ workflows:
               ignore:
                 - /.*/
 {%- else %}
-      - build
+{%- for case in matrix %}
+      - {{ matrix_case_name(case) }}
+{%- endfor -%}
 {%- endif -%}
 {%- endblock %}
 {# #}
diff --git a/conda_smithy/templates/run_docker_build.tmpl b/conda_smithy/templates/run_docker_build.tmpl
index 90d57163f..58c5131ed 100644
--- a/conda_smithy/templates/run_docker_build.tmpl
+++ b/conda_smithy/templates/run_docker_build.tmpl
@@ -1,3 +1,16 @@
+{%- macro matrix_env_vars(a_matrix) -%}
+    {{ '-e HOST_USER_ID="${HOST_USER_ID}" \\' }}
+    {%- set vars_used = [] %}
+    {%- for case in a_matrix -%}
+        {%- for dep, ver in case -%}
+            {%- if dep not in vars_used %}
+                        -e {{ dep }}="${{ "{" }}{{ dep }}{{ "}" }}" \
+                {%- do vars_used.append(dep) -%}
+            {%- endif -%}
+        {%- endfor -%}
+    {%- endfor -%}
+{%- endmacro -%}
+
 #!/usr/bin/env bash
 
 # PLEASE NOTE: This script has been automatically generated by conda-smithy. Any changes here
@@ -40,7 +53,7 @@ rm -f "$FEEDSTOCK_ROOT/build_artefacts/conda-forge-build-done"
 cat << EOF | {{ docker.executable }} run -i \
                         -v "${RECIPE_ROOT}":/recipe_root \
                         -v "${FEEDSTOCK_ROOT}":/feedstock_root \
-                        -e HOST_USER_ID="${HOST_USER_ID}" \
+                        {{ matrix_env_vars(matrix) }}
                         -a stdin -a stdout -a stderr \
                         {{ docker.image }} \
                         {{ docker.command }} || exit 1
@@ -59,12 +72,10 @@ conda install --yes --quiet conda-forge-build-setup
 {% if build_setup -%}
 {{ build_setup }}{% endif -%}
 
-{%- block build %}
 conda build /recipe_root --quiet || exit 1
 {%- for owner, channel in channels['targets'] %}
 {{ upload_script }} /recipe_root {{ owner }} --channel={{ channel }} || exit 1
-{%- endfor -%}
-{%- endblock -%}
+{%- endfor %}
 
 touch /feedstock_root/build_artefacts/conda-forge-build-done
 EOF
diff --git a/conda_smithy/templates/run_docker_build_matrix.tmpl b/conda_smithy/templates/run_docker_build_matrix.tmpl
deleted file mode 100644
index d182cef7d..000000000
--- a/conda_smithy/templates/run_docker_build_matrix.tmpl
+++ /dev/null
@@ -1,19 +0,0 @@
-{%- extends "run_docker_build.tmpl" -%}
-{% macro matrix_env(matrix_item) -%}
-  {%- for dep_name, version in matrix_item %}
-    export {{ dep_name }}={{version }}
-  {%- endfor %}
-{%- endmacro -%}
-
-{%- block build -%}
-  # Embarking on {{ matrix|length }} case(s).
-{%- for case in matrix %}
-  {%- if case %}
-    {{- matrix_env(case) }}
-  {%- endif -%}
-  {{- super()|indent(4) }}
-{% endfor %}{% endblock -%}
-{%- block test_and_upload -%}{% for case in matrix -%}
-    {{ matrix_env(case) }}
-    {{- super()|indent(4) }}
-{%- endfor -%}{% endblock -%}