diff --git a/cmake/Modules/Packages/USER-COLVARS.cmake b/cmake/Modules/Packages/USER-COLVARS.cmake
index 92595a9c8a..408c39c5fe 100644
--- a/cmake/Modules/Packages/USER-COLVARS.cmake
+++ b/cmake/Modules/Packages/USER-COLVARS.cmake
@@ -2,6 +2,8 @@ set(COLVARS_SOURCE_DIR ${LAMMPS_LIB_SOURCE_DIR}/colvars)
 
 file(GLOB COLVARS_SOURCES ${COLVARS_SOURCE_DIR}/[^.]*.cpp)
 
+option(COLVARS_DEBUG "Debugging messages for Colvars (quite verbose)" OFF)
+
 # Build Lepton by default
 option(COLVARS_LEPTON "Build and link the Lepton library" ON)
 
@@ -21,6 +23,11 @@ set_target_properties(colvars PROPERTIES OUTPUT_NAME lammps_colvars${LAMMPS_MACH
 target_include_directories(colvars PUBLIC ${LAMMPS_LIB_SOURCE_DIR}/colvars)
 target_link_libraries(lammps PRIVATE colvars)
 
+if(COLVARS_DEBUG)
+  target_compile_definitions(colvars PRIVATE -DCOLVARS_DEBUG)
+  target_compile_definitions(lammps PRIVATE -DCOLVARS_DEBUG) # For the proxy
+endif()
+
 if(COLVARS_LEPTON)
   target_link_libraries(lammps PRIVATE lepton)
   target_compile_definitions(colvars PRIVATE -DLEPTON)