diff --git a/.circleci/config.yml b/.circleci/config.yml
index 605430fb3f..521aca22ef 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -99,23 +99,35 @@ workflows:
   version: 2
   build:
     jobs:
-      - sytestpy2
-      - sytestpy2postgres
-      - sytestpy3
-      - sytestpy3postgres
+      - sytestpy2:
+          filters:
+            branches:
+              only: /develop|master|release-.*/
+      - sytestpy2postgres:
+          filters:
+            branches:
+              only: /develop|master|release-.*/
+      - sytestpy3:
+          filters:
+            branches:
+              only: /develop|master|release-.*/
+      - sytestpy3postgres:
+          filters:
+            branches:
+              only: /develop|master|release-.*/
       - sytestpy2merged:
           filters:
             branches:
-              ignore: /develop|master/
+              ignore: /develop|master|release-.*/
       - sytestpy2postgresmerged:
           filters:
             branches:
-              ignore: /develop|master/
+              ignore: /develop|master|release-.*/
       - sytestpy3merged:
           filters:
             branches:
-              ignore: /develop|master/
+              ignore: /develop|master|release-.*/
       - sytestpy3postgresmerged:
           filters:
             branches:
-              ignore: /develop|master/
+              ignore: /develop|master|release-.*/
diff --git a/changelog.d/3957.misc b/changelog.d/3957.misc
new file mode 100644
index 0000000000..69d647f119
--- /dev/null
+++ b/changelog.d/3957.misc
@@ -0,0 +1 @@
+CircleCI now only runs merged jobs on PRs, and commit jobs on develop, master, and release branches.
diff --git a/scripts-dev/next_github_number.sh b/scripts-dev/next_github_number.sh
new file mode 100755
index 0000000000..376280025a
--- /dev/null
+++ b/scripts-dev/next_github_number.sh
@@ -0,0 +1,9 @@
+#!/bin/bash
+
+set -e
+
+# Fetch the current GitHub issue number, add one to it -- presto! The likely
+# next PR number.
+CURRENT_NUMBER=`curl -s "https://api.github.com/repos/matrix-org/synapse/issues?state=all&per_page=1" | jq -r ".[0].number"`
+CURRENT_NUMBER=$((CURRENT_NUMBER+1))
+echo $CURRENT_NUMBER
\ No newline at end of file