diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 89eb94db4..d4b520da0 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -485,6 +485,7 @@ class BuildProject:
 
     @lazy_property
     def prefix(self) -> str:
+        # This must be the same as CMakeInterpreter.__init__
         return 'build.' if self.for_machine is MachineChoice.BUILD else ''
 
     @lazy_property
diff --git a/mesonbuild/cmake/interpreter.py b/mesonbuild/cmake/interpreter.py
index ef522dfc3..5e7111563 100644
--- a/mesonbuild/cmake/interpreter.py
+++ b/mesonbuild/cmake/interpreter.py
@@ -795,10 +795,12 @@ class ConverterCustomTarget:
         mlog.log('  -- depends:      ', mlog.bold(str(self.depends)))
 
 class CMakeInterpreter:
-    def __init__(self, subdir: Path, env: 'Environment', backend: 'Backend', for_machine: MachineChoice):
-        self.subdir = subdir
-        self.src_dir = Path(env.get_source_dir(), subdir)
-        self.build_dir_rel = subdir / '__CMake_build'
+    def __init__(self, subdir: str, env: 'Environment', backend: 'Backend', for_machine: MachineChoice):
+        self.subdir = Path(subdir)
+        # This must be the same as BuildProject.prefix
+        prefix = 'build.' if for_machine is MachineChoice.BUILD else ''
+        self.build_dir_rel = Path(prefix + subdir) / '__CMake_build'
+        self.src_dir = Path(env.get_source_dir()) / subdir
         self.build_dir = Path(env.get_build_dir()) / self.build_dir_rel
         self.install_prefix = Path(T.cast('str', env.coredata.optstore.get_value_for(OptionKey('prefix'))))
         self.env = env
diff --git a/mesonbuild/interpreter/interpreter.py b/mesonbuild/interpreter/interpreter.py
index c0e194ff0..0e34256d4 100644
--- a/mesonbuild/interpreter/interpreter.py
+++ b/mesonbuild/interpreter/interpreter.py
@@ -1101,7 +1101,7 @@ class Interpreter(InterpreterBase, HoldableObject):
             from ..modules.cmake import CMakeSubprojectOptions
             kw_opts = kwargs.get('options') or CMakeSubprojectOptions()
             cmake_options = kwargs.get('cmake_options', []) + kw_opts.cmake_options
-            cm_int = CMakeInterpreter(Path(subdir), self.build.environment, self.backend, for_machine)
+            cm_int = CMakeInterpreter(subdir, self.build.environment, self.backend, for_machine)
             cm_int.initialise(cmake_options)
             cm_int.analyse()