diff --git a/dissect/fat/c_exfat.py b/dissect/fat/c_exfat.py
index 9ec94e0..1cda56e 100644
--- a/dissect/fat/c_exfat.py
+++ b/dissect/fat/c_exfat.py
@@ -1,6 +1,6 @@
-from dissect import cstruct
+from dissect.cstruct import cstruct
 
-c_exfat_def = """
+exfat_def = """
 enum entry_types : uint8 {
     allocation_bitmap   = 0x81,
     upcase_table        = 0x82,
@@ -139,8 +139,7 @@
 """
 
 # default endianess is LE so we keep it that way.
-c_exfat = cstruct.cstruct()
-c_exfat.load(c_exfat_def)
+c_exfat = cstruct().load(exfat_def)
 
 EOC = 0xFFFFFFFF  # indicates end of cluster chain
 FID = 0xFFFFFFF8  # indicates start of FAT
diff --git a/dissect/fat/c_fat.py b/dissect/fat/c_fat.py
index f031b55..74eaeb0 100644
--- a/dissect/fat/c_fat.py
+++ b/dissect/fat/c_fat.py
@@ -1,7 +1,7 @@
-from dissect import cstruct
+from dissect.cstruct import cstruct
 
 # https://ogris.de/fatrepair/fat.c
-c_fat_def = """
+fat_def = """
 #define ATTR_READ_ONLY 0x01
 #define ATTR_HIDDEN    0x02
 #define ATTR_SYSTEM    0x04
@@ -90,8 +90,7 @@
 };
 """  # noqa: E501
 
-c_fat = cstruct.cstruct()
-c_fat.load(c_fat_def)
+c_fat = cstruct().load(fat_def)
 
 Fattype = c_fat.Fattype
 
diff --git a/pyproject.toml b/pyproject.toml
index 376f006..12df85a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -25,8 +25,8 @@ classifiers = [
   "Topic :: Utilities",
 ]
 dependencies = [
-    "dissect.cstruct>=3.0.dev,<4.0.dev",
-    "dissect.util>=3.0.dev,<4.0.dev",
+    "dissect.cstruct>=4.dev,<5",
+    "dissect.util>=3,<4",
 ]
 dynamic = ["version"]
 
@@ -35,6 +35,12 @@ homepage = "https://dissect.tools"
 documentation = "https://docs.dissect.tools/en/latest/projects/dissect.fat"
 repository = "https://github.com/fox-it/dissect.fat"
 
+[project.optional-dependencies]
+dev = [
+    "dissect.cstruct>=4.0.dev,<5.0.dev",
+    "dissect.util>=3.0.dev,<4.0.dev",
+]
+
 [tool.black]
 line-length = 120
 
diff --git a/tox.ini b/tox.ini
index 67e8e8a..7bd2890 100644
--- a/tox.ini
+++ b/tox.ini
@@ -11,6 +11,7 @@ minversion = 4.4.3
 requires = virtualenv>=20.16.6
 
 [testenv]
+extras = dev
 deps =
     pytest
     pytest-cov