diff --git a/conans/client/build/cmake.py b/conans/client/build/cmake.py
index 0006d862268..d9a668b37fe 100644
--- a/conans/client/build/cmake.py
+++ b/conans/client/build/cmake.py
@@ -47,8 +47,14 @@ def __init__(self, conanfile, generator=None, cmake_system_name=True,
         :param generator_platform: Generator platform name or none to autodetect (-A cmake option)
         """
         if getattr(conanfile, "must_use_new_helpers", None):
-            raise ConanException("Using the wrong 'CMake' helper. To use CMakeDeps, CMakeToolchain "
-                                 "you should use 'from conan.tools.cmake import CMake'")
+            wrong_helper_msg = "Using the wrong 'CMake' helper. To use CMakeDeps, CMakeToolchain "\
+                               "you should use 'from conan.tools.cmake import CMake'. "\
+                               "Set environment variable CONAN_DISABLE_STRICT_MODE=1 to override "\
+                               "this check (should only be used to build old packages)."
+            if get_env("CONAN_DISABLE_STRICT_MODE", False):
+                conanfile.output.warning(wrong_helper_msg)
+            else:
+                raise ConanException(wrong_helper_msg)
         self._append_vcvars = append_vcvars
         self._conanfile = conanfile
         self._settings = conanfile.settings
diff --git a/conans/client/build/msbuild.py b/conans/client/build/msbuild.py
index 778b81a7628..df8b7bee43a 100644
--- a/conans/client/build/msbuild.py
+++ b/conans/client/build/msbuild.py
@@ -23,9 +23,14 @@ class MSBuild(object):
     def __init__(self, conanfile):
         if isinstance(conanfile, ConanFile):
             if getattr(conanfile, "must_use_new_helpers", None):
-                raise ConanException(
-                    "Using the wrong 'MSBuild' helper. To use MSBuildDeps, MSBuildToolchain "
-                    "you should use 'from conan.tools.microsoft import MSBuild'")
+                wrong_helper_msg = "Using the wrong 'MSBuild' helper. To use MSBuildDeps, MSBuildToolchain "\
+                                   "you should use 'from conan.tools.microsoft import MSBuild'. "\
+                                   "Set environment variable CONAN_DISABLE_STRICT_MODE=1 to override "\
+                                   "this check (should only be used to build old packages)."
+                if get_env("CONAN_DISABLE_STRICT_MODE", False):
+                    conanfile.output.warning(wrong_helper_msg)
+                else:
+                    raise ConanException(wrong_helper_msg)
             self._conanfile = conanfile
             self._settings = self._conanfile.settings
             self._output = self._conanfile.output