diff --git a/dissect/regf/c_regf.py b/dissect/regf/c_regf.py
index 30e1d2c..4bdb4b5 100644
--- a/dissect/regf/c_regf.py
+++ b/dissect/regf/c_regf.py
@@ -1,6 +1,6 @@
-from dissect import cstruct
+from dissect.cstruct import cstruct
 
-c_regf_def = """
+regf_def = """
 struct REGF_HEADER {
     uint32 signature;
     uint32 primary_sequence;
@@ -137,8 +137,7 @@
 };
 """
 
-c_regf = cstruct.cstruct()
-c_regf.load(c_regf_def)
+c_regf = cstruct().load(regf_def)
 
 
 REG_NONE = 0x0
diff --git a/pyproject.toml b/pyproject.toml
index f1416a0..7faad4d 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.regf"
 repository = "https://github.com/fox-it/dissect.regf"
 
+[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