diff --git a/cython/python_solvespace/__init__.py b/cython/python_solvespace/__init__.py
index 7a418578..b2058fda 100644
--- a/cython/python_solvespace/__init__.py
+++ b/cython/python_solvespace/__init__.py
@@ -10,7 +10,6 @@ __license__ = "GPLv3+"
 __email__ = "pyslvs@gmail.com"
 __version__ = "3.0.6"
 
-from enum import IntEnum, auto
 from .slvs import (
     quaternion_u,
     quaternion_v,
@@ -32,51 +31,3 @@ __all__ = [
     'Entity',
     'SolverSystem',
 ]
-
-
-class Constraint(IntEnum):
-    """Symbol of the constraint types."""
-    # Expose macro of constraint types
-    POINTS_COINCIDENT = 100000
-    PT_PT_DISTANCE = auto()
-    PT_PLANE_DISTANCE = auto()
-    PT_LINE_DISTANCE = auto()
-    PT_FACE_DISTANCE = auto()
-    PT_IN_PLANE = auto()
-    PT_ON_LINE = auto()
-    PT_ON_FACE = auto()
-    EQUAL_LENGTH_LINES = auto()
-    LENGTH_RATIO = auto()
-    EQ_LEN_PT_LINE_D = auto()
-    EQ_PT_LN_DISTANCES = auto()
-    EQUAL_ANGLE = auto()
-    EQUAL_LINE_ARC_LEN = auto()
-    SYMMETRIC = auto()
-    SYMMETRIC_HORIZ = auto()
-    SYMMETRIC_VERT = auto()
-    SYMMETRIC_LINE = auto()
-    AT_MIDPOINT = auto()
-    HORIZONTAL = auto()
-    VERTICAL = auto()
-    DIAMETER = auto()
-    PT_ON_CIRCLE = auto()
-    SAME_ORIENTATION = auto()
-    ANGLE = auto()
-    PARALLEL = auto()
-    PERPENDICULAR = auto()
-    ARC_LINE_TANGENT = auto()
-    CUBIC_LINE_TANGENT = auto()
-    EQUAL_RADIUS = auto()
-    PROJ_PT_DISTANCE = auto()
-    WHERE_DRAGGED = auto()
-    CURVE_CURVE_TANGENT = auto()
-    LENGTH_DIFFERENCE = auto()
-
-
-class ResultFlag(IntEnum):
-    """Symbol of the result flags."""
-    # Expose macro of result flags
-    OKAY = 0
-    INCONSISTENT = auto()
-    DIDNT_CONVERGE = auto()
-    TOO_MANY_UNKNOWNS = auto()
diff --git a/cython/python_solvespace/slvs.pxd b/cython/python_solvespace/slvs.pxd
index 430d5364..0394beff 100644
--- a/cython/python_solvespace/slvs.pxd
+++ b/cython/python_solvespace/slvs.pxd
@@ -252,7 +252,7 @@ cdef class SolverSystem:
     cpdef int dof(self)
     cpdef object constraints(self)
     cpdef list failures(self)
-    cpdef int solve(self)
+    cdef int solve_c(self) nogil
 
     cpdef size_t param_len(self)
     cpdef size_t entity_len(self)
diff --git a/cython/python_solvespace/slvs.pyx b/cython/python_solvespace/slvs.pyx
index 1cfa1f00..55db88ba 100644
--- a/cython/python_solvespace/slvs.pyx
+++ b/cython/python_solvespace/slvs.pyx
@@ -10,6 +10,7 @@ email: pyslvs@gmail.com
 """
 
 from cpython.object cimport Py_EQ, Py_NE
+from enum import IntEnum, auto
 from collections import Counter
 
 
@@ -65,6 +66,54 @@ cpdef tuple make_quaternion(double ux, double uy, double uz, double vx, double v
     return qw, qx, qy, qz
 
 
+class Constraint(IntEnum):
+    """Symbol of the constraint types."""
+    # Expose macro of constraint types
+    POINTS_COINCIDENT = 100000
+    PT_PT_DISTANCE = auto()
+    PT_PLANE_DISTANCE = auto()
+    PT_LINE_DISTANCE = auto()
+    PT_FACE_DISTANCE = auto()
+    PT_IN_PLANE = auto()
+    PT_ON_LINE = auto()
+    PT_ON_FACE = auto()
+    EQUAL_LENGTH_LINES = auto()
+    LENGTH_RATIO = auto()
+    EQ_LEN_PT_LINE_D = auto()
+    EQ_PT_LN_DISTANCES = auto()
+    EQUAL_ANGLE = auto()
+    EQUAL_LINE_ARC_LEN = auto()
+    SYMMETRIC = auto()
+    SYMMETRIC_HORIZ = auto()
+    SYMMETRIC_VERT = auto()
+    SYMMETRIC_LINE = auto()
+    AT_MIDPOINT = auto()
+    HORIZONTAL = auto()
+    VERTICAL = auto()
+    DIAMETER = auto()
+    PT_ON_CIRCLE = auto()
+    SAME_ORIENTATION = auto()
+    ANGLE = auto()
+    PARALLEL = auto()
+    PERPENDICULAR = auto()
+    ARC_LINE_TANGENT = auto()
+    CUBIC_LINE_TANGENT = auto()
+    EQUAL_RADIUS = auto()
+    PROJ_PT_DISTANCE = auto()
+    WHERE_DRAGGED = auto()
+    CURVE_CURVE_TANGENT = auto()
+    LENGTH_DIFFERENCE = auto()
+
+
+class ResultFlag(IntEnum):
+    """Symbol of the result flags."""
+    # Expose macro of result flags
+    OKAY = 0
+    INCONSISTENT = auto()
+    DIDNT_CONVERGE = auto()
+    TOO_MANY_UNKNOWNS = auto()
+
+
 cdef class Params:
 
     """Python object to handle multiple parameter handles."""
@@ -384,7 +433,7 @@ cdef class SolverSystem:
         """Return a list of failed constraint numbers."""
         return self.failed_list
 
-    cpdef int solve(self):
+    cdef int solve_c(self) nogil:
         """Start the solving, return the result flag."""
         cdef Slvs_System sys
         # Parameters
@@ -406,6 +455,9 @@ cdef class SolverSystem:
         self.dof_v = sys.dof
         return sys.result
 
+    def solve(self):
+        return ResultFlag(self.solve_c())
+
     cpdef size_t param_len(self):
         """The length of parameter list."""
         return self.param_list.size()