diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index b202f78da..91460218a 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -303,7 +303,7 @@ jobs:
         [conf]
         tools.env.virtualenv:auto_use = True
         tools.build:compiler_executables = {"c": "${{ matrix.compiler.c-path }}", "cpp": "${{ matrix.compiler.cpp-path }}"}
-        tools.build:defines = CFG_ENABLE_TEST_SUITE=ON,JEMALLOC_PREFIX=je_,CMAKE_INSTALL_PREFIX=${{ github.workspace }}/install/${{ matrix.build-type.conan-build-type }} 
+        tools.build:defines = [CFG_ENABLE_TEST_SUITE=ON,JEMALLOC_PREFIX=je_,CMAKE_INSTALL_PREFIX=${{ github.workspace }}/install/${{ matrix.build-type.conan-build-type }}] 
         ${{ matrix.build-and-test-config.conan-profile-custom-conf }}
   
         [buildenv]