diff --git a/test/seqan3-test.cmake b/test/seqan3-test.cmake
index 03148af7b6..74d7bd2c6d 100644
--- a/test/seqan3-test.cmake
+++ b/test/seqan3-test.cmake
@@ -41,6 +41,7 @@ if (SEQAN3_WITH_SEQAN2 OR SEQAN3_WITH_SEQAN2_CI)
     if (SEQAN3_SEQAN2_INCLUDE_DIR)
         message (STATUS "Building tests with SeqAn2.")
         target_include_directories (seqan3_seqan3 SYSTEM INTERFACE ${SEQAN3_SEQAN2_INCLUDE_DIR})
+        target_compile_definitions (seqan3_seqan3 INTERFACE "SEQAN3_HAS_SEQAN2=1")
     else ()
         message (FATAL_ERROR "Could not find SeqAn2.")
     endif ()