diff --git a/tools/toolchains/arm.py b/tools/toolchains/arm.py
index 7ec6bad145..f294edb5f5 100644
--- a/tools/toolchains/arm.py
+++ b/tools/toolchains/arm.py
@@ -31,6 +31,9 @@ class ARM(mbedToolchain):
     DEP_PATTERN = re.compile('\S+:\s(?P<file>.+)\n')
 
 
+    # ANY changes to these default flags is backwards incompatible and require
+    # an update to the mbed-sdk-tools and website that introduces a profile
+    # for the previous version of these flags
     DEFAULT_FLAGS = {
         'common': ["-c", "--gnu",
             "-Otime", "--split_sections", "--apcs=interwork",
diff --git a/tools/toolchains/gcc.py b/tools/toolchains/gcc.py
index c4f41e0f82..04440dd447 100644
--- a/tools/toolchains/gcc.py
+++ b/tools/toolchains/gcc.py
@@ -28,6 +28,9 @@ class GCC(mbedToolchain):
     DIAGNOSTIC_PATTERN = re.compile('((?P<file>[^:]+):(?P<line>\d+):)(\d+:)? (?P<severity>warning|error): (?P<message>.+)')
     INDEX_PATTERN  = re.compile('(?P<col>\s*)\^')
 
+    # ANY changes to these default flags is backwards incompatible and require
+    # an update to the mbed-sdk-tools and website that introduces a profile
+    # for the previous version of these flags
     DEFAULT_FLAGS = {
         'common': ["-c", "-Wall", "-Wextra",
             "-Wno-unused-parameter", "-Wno-missing-field-initializers",
diff --git a/tools/toolchains/iar.py b/tools/toolchains/iar.py
index 447761944d..7c8b5811bc 100644
--- a/tools/toolchains/iar.py
+++ b/tools/toolchains/iar.py
@@ -29,6 +29,9 @@ class IAR(mbedToolchain):
     DIAGNOSTIC_PATTERN = re.compile('"(?P<file>[^"]+)",(?P<line>[\d]+)\s+(?P<severity>Warning|Error)(?P<message>.+)')
     INDEX_PATTERN  = re.compile('(?P<col>\s*)\^')
 
+    # ANY changes to these default flags is backwards incompatible and require
+    # an update to the mbed-sdk-tools and website that introduces a profile
+    # for the previous version of these flags
     DEFAULT_FLAGS = {
         'common': [
             "--no_wrap_diagnostics",