this works

.gitignore

@@ -112,3 +112,6 @@ dmypy.json
 
 # Pyre type checker
 .pyre/
+
+# vscode
+.vscode/

setup.py

@@ -87,9 +87,11 @@ def finalize_options(self):
             if SYSTEM_FITSIO_LIBDIR is not None:
                 self.library_dirs.insert(0, SYSTEM_FITSIO_LIBDIR)
         else:
-            # We defer configuration of the bundled cfitsio to build_extensions
-            # because we will know the compiler there.
-            self.include_dirs.insert(0, self.cfitsio_build_dir)
+            # we put our include dir first to avoid other fitsio install's
+            # header files
+            self.include_dirs.insert(
+                0, os.path.join(".", self.cfitsio_build_dir)
+            )
 
     def run(self):
         # For extensions that require 'numpy' in their include dirs,
@@ -110,13 +112,12 @@ def build_extensions(self):
 
             # Use the compiler for building python to build cfitsio
             # for maximized compatibility.
-            # we put our include dir first to avoid other fitsio install's
-            # header files
-            CCold = self.compiler.compiler
-            self.compiler.compiler = (
-                [CCold[0]]
-                + ["-I%s" % self.cfitsio_build_dir]
-                + CCold[1:]
+
+            # turns out we need to set the include dirs here too
+            # directly for the compiler
+            self.compiler.include_dirs.insert(
+                0,
+                os.path.join(".", self.cfitsio_build_dir),
             )
 
             CCold = self.compiler.compiler