diff --git a/common.py b/common.py
index 2e73455..5c138b2 100644
--- a/common.py
+++ b/common.py
@@ -153,9 +153,6 @@ DOL_SRCDIR = "src"
 # Directory for decompiled rel code
 REL_SRCDIR = "rel"
 
-# Include directory
-INCDIR = "include"
-
 # Build artifacts directory
 BUILDDIR = "build"
 
@@ -279,20 +276,30 @@ REL_FULL = f"{OUTDIR}/rel.s"
 
 ASFLAGS = ' '.join([
     "-m gekko",
-    f"-I {INCDIR}",
     f"-I {PPCDIS_INCDIR}",
     f"-I orig"
 ])
 
+INCDIRS = [
+    PPCDIS_INCDIR,
+    BUILD_INCDIR,
+    f"{SPM_HEADERS}/decomp",
+    f"{SPM_HEADERS}/include"
+]
+MWCC_INCLUDES = ' '.join(f"-i {d}" for d in INCDIRS)
+GCC_INCLUDES = ' '.join(f"-I {d}" for d in INCDIRS)
+
+DEFINES = [
+    "DECOMP",
+    "SPM_EU0"
+]
+MWCC_DEFINES = ' '.join(f"-d {d}" for d in DEFINES)
+GCC_DEFINES = ' '.join(f"-D {d}" for d in DEFINES)
+
 CPPFLAGS = ' '.join([
     "-nostdinc",
-    "-DDECOMP",
-    "-DSPM_EU0",
-    f"-I {INCDIR}",
-    f"-I {PPCDIS_INCDIR}",
-    f"-I {BUILD_INCDIR}",
-    f"-I {SPM_HEADERS}/decomp",
-    f"-I {SPM_HEADERS}/include"
+    GCC_DEFINES,
+    GCC_INCLUDES
 ])
 
 DOL_SDATA2_SIZE = 4
@@ -310,8 +317,7 @@ CFLAGS = [
     "-rostr",
     "-sym dwarf-2",
     "-ipa file",
-    "-d DECOMP",
-    "-d SPM_EU0",
+    MWCC_DEFINES
 ]
 BASE_DOL_CFLAGS = CFLAGS + [
     "-inline all",
@@ -330,11 +336,7 @@ LOCAL_CFLAGS = [
     "-proc gekko",
     "-maxerrors 1",
     "-I-",
-    f"-i {INCDIR}",
-    f"-i {PPCDIS_INCDIR}",
-    f"-i {BUILD_INCDIR}",
-    f"-i {SPM_HEADERS}/decomp",
-    f"-i {SPM_HEADERS}/include",
+    MWCC_INCLUDES
 ]
 DOL_CFLAGS = ' '.join(BASE_DOL_CFLAGS + LOCAL_CFLAGS)
 REL_CFLAGS = ' '.join(BASE_REL_CFLAGS + LOCAL_CFLAGS)
diff --git a/diff_settings.py b/diff_settings.py
index d89ba4f..02cff5e 100644
--- a/diff_settings.py
+++ b/diff_settings.py
@@ -6,12 +6,12 @@ def apply(config, args: Namespace):
         config["mapfile"] = c.REL_MAP
         config["myimg"] = c.REL_PLF
         config["baseimg"] = c.REL_EXPECTED
-        config["source_directories"] = [c.REL_SRCDIR, c.INCDIR]
+        config["source_directories"] = [c.REL_SRCDIR, *c.INCDIRS]
     else:
         config["mapfile"] = c.DOL_MAP
         config["myimg"] = c.DOL_ELF
         config["baseimg"] = c.DOL_EXPECTED
-        config["source_directories"] = [c.DOL_SRCDIR, c.INCDIR]
+        config["source_directories"] = [c.DOL_SRCDIR, *c.INCDIRS]
     config["make_command"] = ["ninja"]
     config["makeflags"] = []
     config["arch"] = "ppc"
diff --git a/makectx.py b/makectx.py
index df50a26..c6f6323 100644
--- a/makectx.py
+++ b/makectx.py
@@ -45,4 +45,4 @@ def makectx(bases: List[str]):
             ret += process_header(header, bases)
     return ret
 
-print(makectx([c.INCDIR, c.PPCDIS_INCDIR]))
+print(makectx(c.INCDIRS))
diff --git a/makectx_m2c.py b/makectx_m2c.py
index 9662ffb..40d6375 100644
--- a/makectx_m2c.py
+++ b/makectx_m2c.py
@@ -20,7 +20,7 @@ def make_includes(dirnames: List[str]) -> str:
     )
 
 # Find all headers
-includes = make_includes([c.INCDIR, c.PPCDIS_INCDIR])
+includes = make_includes(c.INCDIRS)
 
 # Run mwcc preprocessor
 with NamedTemporaryFile(suffix=".c", delete=False) as tmp:
@@ -28,7 +28,7 @@ with NamedTemporaryFile(suffix=".c", delete=False) as tmp:
         tmp.write(includes.encode())
         tmp.close()
         out = c.get_cmd_stdout(
-            f"{c.CC} -I- -i {c.INCDIR} -i {c.PPCDIS}/include -DM2C -stderr -E {tmp.name}"
+            f"{c.CC} -I- {c.MWCC_INCLUDES} {c.MWCC_DEFINES} -d M2C -stderr -E {tmp.name}"
         )
     finally:
         unlink(tmp.name)