diff --git a/ci/test.yml b/ci/test.yml
index b72f6cbbe5..fa5adcd3ee 100644
--- a/ci/test.yml
+++ b/ci/test.yml
@@ -58,8 +58,9 @@ core device test:
     - core unix frozen debug build
   variables:
     TREZOR_PROFILING: 1
+    MULTICORE: 4  # more could interfere with other jobs
   script:
-    - $NIX_SHELL --run "poetry run make -C core test_emu_ui | ts -s"
+    - $NIX_SHELL --run "poetry run make -C core test_emu_ui_multicore | ts -s"
   after_script:
     - mv core/src/.coverage core/.coverage.test_emu
     - mv tests/ui_tests/reports/test/ test_ui_report
diff --git a/core/Makefile b/core/Makefile
index 3045d51419..d93063de7d 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -60,6 +60,8 @@ PYTEST = pytest --junitxml=$(JUNIT_XML)
 TREZOR_FIDO2_UDP_PORT = 21326
 RUST_TARGET=$(shell rustc -vV | sed -n 's/host: //p')
 
+MULTICORE ?= "auto"
+
 ## help commands:
 
 help: ## show this help
@@ -90,7 +92,7 @@ test_emu: ## run selected device tests from python-trezor
 	$(EMU_TEST) $(PYTEST) $(TESTPATH)/device_tests $(TESTOPTS)
 
 test_emu_multicore: ## run device tests using multiple cores
-	$(PYTEST) -n auto $(TESTPATH)/device_tests $(TESTOPTS) --control-emulators --model=core --random-order-seed=$(shell echo $$RANDOM)
+	$(PYTEST) -n $(MULTICORE) $(TESTPATH)/device_tests $(TESTOPTS) --control-emulators --model=core --random-order-seed=$(shell echo $$RANDOM)
 
 test_emu_monero: ## run selected monero device tests from monero-agent
 	cd tests ; $(EMU_TEST) ./run_tests_device_emu_monero.sh $(TESTOPTS)
@@ -114,7 +116,7 @@ test_emu_ui: ## run ui integration tests
 		--ui=test --ui-check-missing --record-text-layout
 
 test_emu_ui_multicore: ## run ui integration tests using multiple cores
-	$(PYTEST) -n auto $(TESTPATH)/device_tests $(TESTOPTS) \
+	$(PYTEST) -n $(MULTICORE) $(TESTPATH)/device_tests $(TESTOPTS) \
 		--ui=test --ui-check-missing --record-text-layout \
 		--control-emulators --model=core --random-order-seed=$(shell echo $$RANDOM)