diff --git a/cmake/VERSION b/cmake/VERSION
index ff313b8c..0cbfaed0 100644
--- a/cmake/VERSION
+++ b/cmake/VERSION
@@ -1 +1 @@
-3.8.4
+3.8.5
diff --git a/cmake/ecbuild_add_library.cmake b/cmake/ecbuild_add_library.cmake
index 03552bed..eeb6a95e 100644
--- a/cmake/ecbuild_add_library.cmake
+++ b/cmake/ecbuild_add_library.cmake
@@ -360,11 +360,15 @@ function( ecbuild_add_library_impl )
       if( "${_p_TYPE}" STREQUAL LIBS )
         target_link_libraries( ${_PAR_TARGET} ${_p_INTF} ${deps} )
         ecbuild_debug("ecbuild_add_library(${_PAR_TARGET}): linking with [${deps}] ${_p_INTF}")
-        ecbuild_debug("ecbuild_add_library(${_PAR_TARGET}): [${skipped_deps}] not found - not linking ${_p_INTF}")
+        if( skipped_deps )
+            ecbuild_debug("ecbuild_add_library(${_PAR_TARGET}): [${skipped_deps}] not found - not linking ${_p_INTF}")
+        endif()
       else()
         target_include_directories( ${_PAR_TARGET} ${_p_INTF} ${deps} )
         ecbuild_debug("ecbuild_add_library(${_PAR_TARGET}): add [${deps}] to include_directories ${_p_INTF}")
-        ecbuild_debug("ecbuild_add_library(${_PAR_TARGET}): [${skipped_deps}] not found - not adding to include_directories ${_p_INTF}")
+        if( skipped_deps )
+            ecbuild_debug("ecbuild_add_library(${_PAR_TARGET}): [${skipped_deps}] not found - not adding to include_directories ${_p_INTF}")
+        endif()
       endif()
     endfunction()
 
@@ -581,8 +585,8 @@ function( ecbuild_add_library_impl )
 
     # add definitions to compilation
     if( DEFINED _PAR_PUBLIC_DEFINITIONS )
-      target_compile_definitions(${_PAR_TARGET} PUBLIC ${_PAR_PUBLIC_DEFINITIONS})
-      ecbuild_debug("ecbuild_add_library(${_PAR_TARGET}): adding PUBLIC definitions ${_PAR_PUBLIC_DEFINITIONS}")
+      target_compile_definitions(${_PAR_TARGET} ${_PUBLIC_INTF} ${_PAR_PUBLIC_DEFINITIONS})
+      ecbuild_debug("ecbuild_add_library(${_PAR_TARGET}): adding ${_PUBLIC_INTF} definitions ${_PAR_PUBLIC_DEFINITIONS}")
     endif()
     if( DEFINED _PAR_PRIVATE_DEFINITIONS )
       target_compile_definitions(${_PAR_TARGET} PRIVATE ${_PAR_PRIVATE_DEFINITIONS})
@@ -590,7 +594,7 @@ function( ecbuild_add_library_impl )
     endif()
     if( DEFINED _PAR_DEFINITIONS )
       if( _PAR_TYPE MATCHES "INTERFACE" )
-        target_compile_definitions(${_PAR_TARGET} PUBLIC ${_PAR_DEFINITIONS})
+        target_compile_definitions(${_PAR_TARGET} INTERFACE ${_PAR_DEFINITIONS})
       else()
         target_compile_definitions(${_PAR_TARGET} PRIVATE ${_PAR_DEFINITIONS})
       endif()
diff --git a/cmake/ecbuild_policies.cmake b/cmake/ecbuild_policies.cmake
index 4e835859..41f57bf1 100644
--- a/cmake/ecbuild_policies.cmake
+++ b/cmake/ecbuild_policies.cmake
@@ -43,4 +43,9 @@ if( POLICY CMP0074 )
     cmake_policy( SET CMP0074 NEW )
 endif()
 
+# Detect invalid indices in the ``list()`` command, new in version 3.21
+if( POLICY CMP0121 )
+    cmake_policy( SET CMP0121 NEW )
+endif()
+
 endif()
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 91b72e52..472c97c3 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -9,3 +9,4 @@ add_subdirectory( ecbuild_add_flags )
 add_subdirectory( find_ecbuild )
 add_subdirectory( project_import )
 add_subdirectory( ecbuild_shared_libs )
+add_subdirectory( interface_library )
diff --git a/tests/ecbuild_add_option/test_project/CMakeLists.txt b/tests/ecbuild_add_option/test_project/CMakeLists.txt
index 388e0c39..32e13518 100644
--- a/tests/ecbuild_add_option/test_project/CMakeLists.txt
+++ b/tests/ecbuild_add_option/test_project/CMakeLists.txt
@@ -3,8 +3,6 @@ cmake_minimum_required(VERSION 3.11 FATAL_ERROR)
 find_package( ecbuild REQUIRED )
 project( test_add_option VERSION 0.1.0 LANGUAGES NONE )
 
-list(INSERT 0 CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
-
 ecbuild_add_option(FEATURE TEST_A) # should default to ON
 ecbuild_add_option(FEATURE TEST_B DEFAULT ON)
 ecbuild_add_option(FEATURE TEST_C DEFAULT OFF)
diff --git a/tests/interface_library/.gitignore b/tests/interface_library/.gitignore
new file mode 100644
index 00000000..a7ff190f
--- /dev/null
+++ b/tests/interface_library/.gitignore
@@ -0,0 +1,2 @@
+build_test_interface_library
+install_test_interface_library
diff --git a/tests/interface_library/CMakeLists.txt b/tests/interface_library/CMakeLists.txt
new file mode 100644
index 00000000..37d6e123
--- /dev/null
+++ b/tests/interface_library/CMakeLists.txt
@@ -0,0 +1,7 @@
+
+ecbuild_add_test(
+  TARGET     test_ecbuild_interface_library
+  TYPE       SCRIPT
+  COMMAND    ${CMAKE_CURRENT_SOURCE_DIR}/build-and-run.sh
+  ENVIRONMENT CMAKE_CURRENT_SOURCE_DIR=${CMAKE_CURRENT_SOURCE_DIR} CMAKE_CURRENT_BINARY_DIR=${CMAKE_CURRENT_BINARY_DIR}
+)
diff --git a/tests/interface_library/build-and-run.sh b/tests/interface_library/build-and-run.sh
new file mode 100755
index 00000000..fd4a7172
--- /dev/null
+++ b/tests/interface_library/build-and-run.sh
@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+
+set -e
+
+HERE=${CMAKE_CURRENT_BINARY_DIR:-"$( cd $( dirname "${BASH_SOURCE[0]}" ) && pwd -P )"}
+SOURCE=${CMAKE_CURRENT_SOURCE_DIR:-$HERE}
+
+# Add ecbuild to path
+export PATH=$SOURCE/../../bin:$PATH
+echo $PATH
+echo $SOURCE
+
+run_test() {
+
+    local tname=$1
+    local exp_sts=$2
+    shift 2
+
+    local bdir=$HERE/build_$tname
+    local idir=$HERE/install_$tname
+    local logf=$HERE/$tname.log
+
+    mkdir -p $bdir && cd $bdir
+    local sts=0
+    echo "Running test '$tname'"
+    ecbuild --prefix=$idir  -- -Wno-deprecated $* $SOURCE/test_project >$logf 2>&1 || sts=$?
+
+    make install
+
+    if [[ $sts -ne $exp_sts ]] ; then
+        echo "Test '$tname': expected exit code $exp_sts, got $sts"
+        cat $logf
+        exit 1
+    fi
+}
+
+# --------------------- cleanup ------------------------
+$SOURCE/clean.sh
+
+# ---------------------- tests -------------------------
+run_test test_interface_library 0
diff --git a/tests/interface_library/clean.sh b/tests/interface_library/clean.sh
new file mode 100755
index 00000000..fb48fcf8
--- /dev/null
+++ b/tests/interface_library/clean.sh
@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+set -e
+
+HERE=${CMAKE_CURRENT_BINARY_DIR:-"$( cd $( dirname "${BASH_SOURCE[0]}" ) && pwd -P )"}
+
+# --------------------- cleanup ------------------------
+echo "cleaning $HERE"
+rm -rf $HERE/build_* $HERE/*.log
diff --git a/tests/interface_library/test_project/CMakeLists.txt b/tests/interface_library/test_project/CMakeLists.txt
new file mode 100644
index 00000000..83b77515
--- /dev/null
+++ b/tests/interface_library/test_project/CMakeLists.txt
@@ -0,0 +1,13 @@
+cmake_minimum_required(VERSION 3.17 FATAL_ERROR)
+
+find_package( ecbuild REQUIRED )
+project( test_interface_library VERSION 0.1.0 LANGUAGES C )
+
+ecbuild_add_library( TARGET intfb_lib TYPE INTERFACE
+                     PUBLIC_INCLUDES 
+                        $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+                        $ENV{HOME}
+                     PUBLIC_LIBS some_lib
+                     PUBLIC_DEFINITIONS MYDEF=1
+                    )
+ecbuild_install_project( NAME test_interface_library )