diff --git a/tools/build_api.py b/tools/build_api.py
index 208547d0f0f..cfa15de4028 100755
--- a/tools/build_api.py
+++ b/tools/build_api.py
@@ -46,7 +46,6 @@
 from .targets import TARGET_NAMES, TARGET_MAP, CORE_ARCH, Target
 from .libraries import Library
 from .toolchains import TOOLCHAIN_CLASSES, TOOLCHAIN_PATHS
-from .toolchains.arm import ARMC5_MIGRATION_WARNING
 from .toolchains.arm import UARM_TOOLCHAIN_WARNING
 from .config import Config
 
@@ -242,9 +241,11 @@ def find_valid_toolchain(target, toolchain):
             ).format(toolchain_name, search_path)
         else:            
             if toolchain_name == "ARMC5":
-                end_warnings.append(ARMC5_MIGRATION_WARNING)
+                raise NotSupportedException(
+                    "Arm Compiler 5 is no longer supported, please upgrade to Arm Compiler 6."
+                )                
             if (
-                toolchain_name in ["uARM", "ARMC5", "ARMC6"] 
+                toolchain_name in ["uARM", "ARMC6"] 
                 and "uARM" in {toolchain_name, target.default_toolchain}
             ):
                 end_warnings.append(UARM_TOOLCHAIN_WARNING)
diff --git a/tools/toolchains/arm.py b/tools/toolchains/arm.py
index 9c46b4514ca..0afd81535c5 100644
--- a/tools/toolchains/arm.py
+++ b/tools/toolchains/arm.py
@@ -29,14 +29,6 @@
 from tools.utils import mkdir, NotSupportedException, run_cmd
 from tools.resources import FileRef
 
-ARMC5_MIGRATION_WARNING = (
-    "Warning: We noticed that you are using Arm Compiler 5. "
-    "We are deprecating the use of Arm Compiler 5. "
-    "Please upgrade your environment to Arm Compiler 6 "
-    "which is free to use with Mbed OS. For more information, "
-    "please visit https://os.mbed.com/docs/mbed-os/latest/tools/index.html"
-)
-
 UARM_TOOLCHAIN_WARNING = (
     "Warning: We noticed that you are using uARM Toolchain either via --toolchain command line or default_toolchain option. "
     "We are deprecating the use of the uARM Toolchain. "