diff --git a/Jenkinsfile b/Jenkinsfile
index 1f38df0..7f777f0 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -48,16 +48,18 @@ pipeline {
                     steps {
                         script {
                             params.LIBRARIES.split().each { LIBRARY ->
-                                stage(name: "${LIBRARY}", concurrency: 1) {
+                                stage("${LIBRARY}") {
                                     parallel params.R7RS_SCHEMES.collectEntries().each { SCHEME ->
                                         [(SCHEME): {
-                                            def IMG="${SCHEME}:head"
-                                            if("${SCHEME}" == "chicken") {
-                                                IMG="${SCHEME}:5"
-                                            }
-                                            stage("${SCHEME} - ${LIBRARY}") {
-                                                catchError(buildResult: 'SUCCESS', stageResult: 'FAILURE') {
-                                                    sh "timeout 600 make SCHEME=${SCHEME} LIBRARY=${LIBRARY} test-r7rs-docker"
+                                            lock {
+                                                def IMG="${SCHEME}:head"
+                                                if("${SCHEME}" == "chicken") {
+                                                    IMG="${SCHEME}:5"
+                                                }
+                                                stage("${SCHEME} - ${LIBRARY}") {
+                                                    catchError(buildResult: 'SUCCESS', stageResult: 'FAILURE') {
+                                                        sh "timeout 600 make SCHEME=${SCHEME} LIBRARY=${LIBRARY} test-r7rs-docker"
+                                                    }
                                                 }
                                             }
                                         }]