diff --git a/UNITTESTS/CMakeLists.txt b/UNITTESTS/CMakeLists.txt
index 95806c5..4116426 100644
--- a/UNITTESTS/CMakeLists.txt
+++ b/UNITTESTS/CMakeLists.txt
@@ -9,10 +9,10 @@
 macro(use_cxx14)
     if (CMAKE_VERSION VERSION_LESS 3.1)
         if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++98")
+            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++14")
         endif()
     else()
-        set(CMAKE_CXX_STANDARD 98)
+        set(CMAKE_CXX_STANDARD 14)
         set(CMAKE_CXX_STANDARD_REQUIRED ON)
     endif()
 endmacro()
diff --git a/UNITTESTS/stubs/ATHandler_stub.cpp b/UNITTESTS/stubs/ATHandler_stub.cpp
index 8f4038f..b69fe50 100644
--- a/UNITTESTS/stubs/ATHandler_stub.cpp
+++ b/UNITTESTS/stubs/ATHandler_stub.cpp
@@ -55,7 +55,7 @@
 bool ATHandler_stub::process_oob_urc = false;
 
 int ATHandler_stub::read_string_index = kRead_string_table_size;
-const char *ATHandler_stub::read_string_table[kRead_string_table_size] = {'\0'};
+const char *ATHandler_stub::read_string_table[kRead_string_table_size];
 int ATHandler_stub::resp_stop_success_count = kResp_stop_count_default;
 
 bool ATHandler_stub::get_debug_flag = false;
diff --git a/features/cellular/framework/AT/AT_CellularSMS.cpp b/features/cellular/framework/AT/AT_CellularSMS.cpp
index dd30b4d..aae8ab5 100644
--- a/features/cellular/framework/AT/AT_CellularSMS.cpp
+++ b/features/cellular/framework/AT/AT_CellularSMS.cpp
@@ -41,7 +41,7 @@
 #define NVAM '?' // Not Valid ascii, ISO-8859-1 mark
 
 // mapping table from 7-bit GSM to ascii (ISO-8859-1)
-static const char gsm_to_ascii[] = {
+static const unsigned char gsm_to_ascii[] = {
     64,     // 0
     163,    // 1
     36,     // 2
@@ -1153,7 +1153,7 @@
     char *gsm_str = new char[len];
     for (uint16_t y = 0; y < len; y++) {
         for (int x = 0; x < GSM_TO_ASCII_TABLE_SIZE; x++) {
-            if (gsm_to_ascii[x] == str[y]) {
+            if (gsm_to_ascii[x] == static_cast<unsigned char>(str[y])) {
                 gsm_str[y] = x;
             }
         }