diff --git a/o2.sh b/o2.sh
index 7688c6bea5..8c7bf85fdb 100644
--- a/o2.sh
+++ b/o2.sh
@@ -134,7 +134,7 @@ valid_defaults:
 ---
 #!/bin/sh
 export ROOTSYS=$ROOT_ROOT
-
+CMAKE_BUILD_TYPE=DEBUG
 # Making sure people do not have SIMPATH set when they build fairroot.
 # Unfortunately SIMPATH seems to be hardcoded in a bunch of places in
 # fairroot, so this really should be cleaned up in FairRoot itself for
diff --git a/o2physics.sh b/o2physics.sh
index 307ad65425..085b9e8974 100644
--- a/o2physics.sh
+++ b/o2physics.sh
@@ -19,7 +19,7 @@ incremental_recipe: |
   mkdir -p $INSTALLROOT/etc/modulefiles && rsync -a --delete etc/modulefiles/ $INSTALLROOT/etc/modulefiles
 ---
 #!/bin/sh
-
+CMAKE_BUILD_TYPE=DEBUG
 if [[ $ALIBUILD_O2PHYSICS_TESTS ]]; then
   # Impose extra errors.
   CXXFLAGS="${CXXFLAGS} -Werror -Wno-error=deprecated-declarations"