diff --git a/UNITTESTS/stubs/connectivity/CMakeLists.txt b/UNITTESTS/stubs/connectivity/CMakeLists.txt
index faba2e38e2d..4f207f24e00 100644
--- a/UNITTESTS/stubs/connectivity/CMakeLists.txt
+++ b/UNITTESTS/stubs/connectivity/CMakeLists.txt
@@ -13,6 +13,7 @@ target_compile_definitions(mbed-stubs-connectivity
         MBED_CONF_LORA_OVER_THE_AIR_ACTIVATION=true
         MBED_CONF_LORA_AUTOMATIC_UPLINK_MESSAGE=true
         MBED_CONF_LORA_TX_MAX_SIZE=255
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
         MDMTXD=NC
         MDMRXD=NC
 )
diff --git a/connectivity/cellular/include/cellular/framework/API/ATHandler.h b/connectivity/cellular/include/cellular/framework/API/ATHandler.h
index 5010b9a0e14..6ba6562fbe4 100644
--- a/connectivity/cellular/include/cellular/framework/API/ATHandler.h
+++ b/connectivity/cellular/include/cellular/framework/API/ATHandler.h
@@ -50,8 +50,6 @@ class FileHandle;
 extern const char *OK;
 extern const char *CRLF;
 
-#define BUFF_SIZE 32
-
 /* AT Error types enumeration */
 enum DeviceErrorType {
     DeviceErrorTypeNoError = 0,
@@ -114,7 +112,7 @@ class ATHandler {
 
     /** Set callback function for URC
      *
-     *  @param prefix   URC text to look for, e.g. "+CMTI:". Maximum length is BUFF_SIZE.
+     *  @param prefix   URC text to look for, e.g. "+CMTI:". Maximum length is MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE.
      *  @param callback function to call on prefix, or 0 to remove callback
      */
     void set_urc_handler(const char *prefix, Callback<void()> callback);
@@ -601,7 +599,7 @@ class ATHandler {
     bool _is_fh_usable;
 
     // should fit any prefix and int
-    char _recv_buff[BUFF_SIZE];
+    char _recv_buff[MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE];
     // reading position
     size_t _recv_len;
     // reading length
@@ -630,7 +628,7 @@ class ATHandler {
     size_t _max_resp_length;
 
     // prefix set during resp_start and used to try matching possible information responses
-    char _info_resp_prefix[BUFF_SIZE];
+    char _info_resp_prefix[MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE];
     bool _debug_on;
     bool _cmd_start;
     bool _use_delimiter;
@@ -640,7 +638,7 @@ class ATHandler {
     // eventqueue event id
     int _event_id;
 
-    char _cmd_buffer[BUFF_SIZE];
+    char _cmd_buffer[MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE];
 };
 
 } // namespace mbed
diff --git a/connectivity/cellular/mbed_lib.json b/connectivity/cellular/mbed_lib.json
index 616a052f20d..c8a24fc2cd4 100644
--- a/connectivity/cellular/mbed_lib.json
+++ b/connectivity/cellular/mbed_lib.json
@@ -44,6 +44,10 @@
         "plmn-fallback-auto" : {
             "help": "If manual PLMN is selected, use mode 4 manual/automatic in AT+COPS to try automatic mode if manual selection fails. Set to null to disable",
             "value": null
+        },
+        "at-handler-buffer-size" : {
+            "help": "Size of the AT handler buffer",
+            "value": 32
         }
     }
 }
diff --git a/connectivity/cellular/source/framework/device/ATHandler.cpp b/connectivity/cellular/source/framework/device/ATHandler.cpp
index c504b1f038d..a3009e70fcd 100644
--- a/connectivity/cellular/source/framework/device/ATHandler.cpp
+++ b/connectivity/cellular/source/framework/device/ATHandler.cpp
@@ -683,7 +683,7 @@ int32_t ATHandler::read_int()
         return -1;
     }
 
-    char buff[BUFF_SIZE];
+    char buff[MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE];
     if (read_string(buff, sizeof(buff)) == 0) {
         return -1;
     }
@@ -960,7 +960,7 @@ void ATHandler::resp_start(const char *prefix, bool stop)
     (void)fill_buffer(false);
 
     if (prefix) {
-        MBED_ASSERT(strlen(prefix) < BUFF_SIZE);
+        MBED_ASSERT(strlen(prefix) < MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE);
         strcpy(_info_resp_prefix, prefix); // copy prefix so we can later use it without having to provide again for info_resp
     }
 
@@ -1225,7 +1225,7 @@ void ATHandler::handle_start(const char *cmd, const char *cmd_chr)
     if (cmd_chr) {
         cmd_char_len = strlen(cmd_chr);
     }
-    MBED_ASSERT((3 + strlen(cmd) + cmd_char_len) < BUFF_SIZE);
+    MBED_ASSERT((3 + strlen(cmd) + cmd_char_len) < MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE);
 
     memcpy(_cmd_buffer + len, cmd, strlen(cmd));
     len += strlen(cmd);
@@ -1258,7 +1258,7 @@ void ATHandler::cmd_start_stop(const char *cmd, const char *cmd_chr, const char
 
 nsapi_error_t ATHandler::at_cmd_str(const char *cmd, const char *cmd_chr, char *resp_buf, size_t buf_size, const char *format, ...)
 {
-    MBED_ASSERT(strlen(cmd) < BUFF_SIZE);
+    MBED_ASSERT(strlen(cmd) < MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE);
     lock();
 
     handle_start(cmd, cmd_chr);
diff --git a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularcontext/CMakeLists.txt b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularcontext/CMakeLists.txt
index 5772d7cf458..0daa233d6c9 100644
--- a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularcontext/CMakeLists.txt
+++ b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularcontext/CMakeLists.txt
@@ -12,6 +12,7 @@ target_compile_definitions(${TEST_NAME}
         MBED_CONF_CELLULAR_USE_SMS=1
         MBED_CONF_NSAPI_DEFAULT_CELLULAR_APN=NULL
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}
diff --git a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellulardevice/CMakeLists.txt b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellulardevice/CMakeLists.txt
index bdf0e684142..e065e68a141 100644
--- a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellulardevice/CMakeLists.txt
+++ b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellulardevice/CMakeLists.txt
@@ -18,6 +18,7 @@ target_compile_definitions(${TEST_NAME}
         MDMRXD=NC
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
         MBED_CONF_CELLULAR_USE_SMS=1
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}
diff --git a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularinformation/CMakeLists.txt b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularinformation/CMakeLists.txt
index 6a28c2556d6..b7a6ec83f7d 100644
--- a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularinformation/CMakeLists.txt
+++ b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularinformation/CMakeLists.txt
@@ -10,6 +10,7 @@ target_compile_definitions(${TEST_NAME}
         DEVICE_SERIAL=1
         DEVICE_INTERRUPTIN=1
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}
diff --git a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularnetwork/CMakeLists.txt b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularnetwork/CMakeLists.txt
index 459172dc62d..70d33ecdc02 100644
--- a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularnetwork/CMakeLists.txt
+++ b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularnetwork/CMakeLists.txt
@@ -10,6 +10,7 @@ target_compile_definitions(${TEST_NAME}
         DEVICE_SERIAL=1
         DEVICE_INTERRUPTIN=1
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}
diff --git a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularsms/CMakeLists.txt b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularsms/CMakeLists.txt
index 3278e53bd1a..2f62b64f8d5 100644
--- a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularsms/CMakeLists.txt
+++ b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularsms/CMakeLists.txt
@@ -11,6 +11,7 @@ target_compile_definitions(${TEST_NAME}
         DEVICE_INTERRUPTIN=1
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
         MBED_CONF_CELLULAR_USE_SMS=1
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}
diff --git a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularstack/CMakeLists.txt b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularstack/CMakeLists.txt
index ca26a782c4c..79c69ea85ae 100644
--- a/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularstack/CMakeLists.txt
+++ b/connectivity/cellular/tests/UNITTESTS/framework/AT/at_cellularstack/CMakeLists.txt
@@ -10,6 +10,7 @@ target_compile_definitions(${TEST_NAME}
         DEVICE_SERIAL=1
         DEVICE_INTERRUPTIN=1
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}
diff --git a/connectivity/cellular/tests/UNITTESTS/framework/device/athandler/CMakeLists.txt b/connectivity/cellular/tests/UNITTESTS/framework/device/athandler/CMakeLists.txt
index 3b0e7e6ba35..9ea7f085230 100644
--- a/connectivity/cellular/tests/UNITTESTS/framework/device/athandler/CMakeLists.txt
+++ b/connectivity/cellular/tests/UNITTESTS/framework/device/athandler/CMakeLists.txt
@@ -12,6 +12,7 @@ target_compile_definitions(${TEST_NAME}
         DEVICE_SERIAL=1
         DEVICE_INTERRUPTIN=1
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}
diff --git a/connectivity/cellular/tests/UNITTESTS/framework/device/cellularcontext/CMakeLists.txt b/connectivity/cellular/tests/UNITTESTS/framework/device/cellularcontext/CMakeLists.txt
index b02db309e4b..c774d6ce2ef 100644
--- a/connectivity/cellular/tests/UNITTESTS/framework/device/cellularcontext/CMakeLists.txt
+++ b/connectivity/cellular/tests/UNITTESTS/framework/device/cellularcontext/CMakeLists.txt
@@ -18,6 +18,7 @@ target_compile_definitions(${TEST_NAME}
         DEVICE_SERIAL=1
         DEVICE_INTERRUPTIN=1
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}
diff --git a/connectivity/cellular/tests/UNITTESTS/framework/device/cellulardevice/CMakeLists.txt b/connectivity/cellular/tests/UNITTESTS/framework/device/cellulardevice/CMakeLists.txt
index 609015a25ed..b903eb08683 100644
--- a/connectivity/cellular/tests/UNITTESTS/framework/device/cellulardevice/CMakeLists.txt
+++ b/connectivity/cellular/tests/UNITTESTS/framework/device/cellulardevice/CMakeLists.txt
@@ -16,6 +16,7 @@ target_compile_definitions(${TEST_NAME}
         DEVICE_SERIAL=1
         DEVICE_INTERRUPTIN=1
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}
diff --git a/connectivity/cellular/tests/UNITTESTS/framework/device/cellularstatemachine/CMakeLists.txt b/connectivity/cellular/tests/UNITTESTS/framework/device/cellularstatemachine/CMakeLists.txt
index 21953781848..00d3b3bd42d 100644
--- a/connectivity/cellular/tests/UNITTESTS/framework/device/cellularstatemachine/CMakeLists.txt
+++ b/connectivity/cellular/tests/UNITTESTS/framework/device/cellularstatemachine/CMakeLists.txt
@@ -17,6 +17,7 @@ target_compile_definitions(${TEST_NAME}
         DEVICE_SERIAL=1
         DEVICE_INTERRUPTIN=1
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}
diff --git a/connectivity/netsocket/tests/UNITTESTS/netsocket/CellularNonIPSocket/CMakeLists.txt b/connectivity/netsocket/tests/UNITTESTS/netsocket/CellularNonIPSocket/CMakeLists.txt
index 214d1abf448..cc1022d152f 100644
--- a/connectivity/netsocket/tests/UNITTESTS/netsocket/CellularNonIPSocket/CMakeLists.txt
+++ b/connectivity/netsocket/tests/UNITTESTS/netsocket/CellularNonIPSocket/CMakeLists.txt
@@ -11,7 +11,7 @@ target_compile_definitions(${TEST_NAME}
         DEVICE_SERIAL=1
         DEVICE_INTERRUPTIN=1
         MBED_CONF_PLATFORM_DEFAULT_SERIAL_BAUD_RATE=115200
-
+        MBED_CONF_CELLULAR_AT_HANDLER_BUFFER_SIZE=32
 )
 
 target_sources(${TEST_NAME}