diff --git a/CMakeLists.txt b/CMakeLists.txt
index b88b55783a..d6f8e23093 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -49,8 +49,15 @@ include_directories(${CRYPTO_INCLUDE_DIRS})
 # Check if asn1c is installed, and check if it supports all options we need
 # a user can provide ASN1C_EXEC to override an asn1c to use (e.g., parallel
 # installation)
-find_program(ASN1C_EXEC_PATH asn1c)
+find_program(ASN1C_EXEC_PATH asn1c HINTS /opt/asn1c/bin)
 set(ASN1C_EXEC ${ASN1C_EXEC_PATH} CACHE FILEPATH "path to asn1c executable")
+if(NOT ASN1C_EXEC)
+    message(FATAL_ERROR "No asn1c found!
+You might want to re-run ./build_oai -I
+Or provide a path to asn1c using
+./build_oai ... --cmake-opt -DASN1C_EXEC=/path/to/asn1c
+")
+endif()
 check_option(${ASN1C_EXEC} -gen-APER ASN1C_EXEC)
 check_option(${ASN1C_EXEC} -no-gen-UPER ASN1C_EXEC)
 check_option(${ASN1C_EXEC} -no-gen-JER ASN1C_EXEC)
diff --git a/cmake_targets/tools/build_helper b/cmake_targets/tools/build_helper
index 303bb2a84d..ef0c52af78 100755
--- a/cmake_targets/tools/build_helper
+++ b/cmake_targets/tools/build_helper
@@ -684,7 +684,7 @@ install_asn1c_from_source(){
     cd /tmp/asn1c
     git checkout vlm_master
     autoreconf -iv
-    ./configure
+    ./configure --prefix /opt/asn1c/
     make -j`nproc`
     $SUDO make install
     cd -