diff --git a/.github/workflows/build-wheels.yml b/.github/workflows/build-wheels.yml
index 4883822d..0e3d72a6 100644
--- a/.github/workflows/build-wheels.yml
+++ b/.github/workflows/build-wheels.yml
@@ -52,6 +52,7 @@ jobs:
         uses: pypa/cibuildwheel@v2.21.3
         env:
           CIBW_BUILD: ${{ matrix.python }}-${{ matrix.buildplat[1] }}*
+          CIBW_MANYLINUX_X86_64_IMAGE: manylinux_2_28
           CIBW_ARCHS: ${{ matrix.buildplat[2] }}
           CIBW_ENVIRONMENT_MACOS: MACOSX_DEPLOYMENT_TARGET=13.0
           CIBW_ENVIRONMENT_PASS_LINUX: RUNNER_OS
diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index f11532f6..02bb25ea 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -40,6 +40,7 @@ list(APPEND tests
     issue306_allocatable_realloc
     issue307_logical_array
     issue32
+    issue373_optional_constructor
     issue41_abstract_classes
     keep_single_interface
     keyword_renaming_issue160
diff --git a/examples/Makefile b/examples/Makefile
index 1f116c8b..a2373099 100644
--- a/examples/Makefile
+++ b/examples/Makefile
@@ -41,6 +41,7 @@ EXAMPLES = \
 	issue32 \
 	issue353_selected_kind \
 	issue357_name_conflict \
+	issue373_optional_constructor \
 	issue41_abstract_classes \
 	keep_single_interface \
 	keyword_renaming_issue160 \
diff --git a/examples/issue373_optional_constructor/Makefile b/examples/issue373_optional_constructor/Makefile
new file mode 100644
index 00000000..88ce63ea
--- /dev/null
+++ b/examples/issue373_optional_constructor/Makefile
@@ -0,0 +1,33 @@
+#=======================================================================
+#                   define the compiler names
+#=======================================================================
+
+include ../make.inc
+PY_MOD      = pywrapper
+F90_SRC     = main.f90
+OBJ         = $(F90_SRC:.f90=.o)
+F90WRAP_SRC = $(addprefix f90wrap_,${F90_SRC})
+WRAPFLAGS   = -v
+F2PY        = f2py-f90wrap
+SRC_AR      = libsrc.a
+.PHONY: all clean
+
+all: test
+
+clean:
+	rm -rf *.mod *.smod *.o ${SRC_AR} f90wrap*.f90 ${PY_MOD}.py _${PY_MOD}*.so __pycache__/ .f2py_f2cmap build ${PY_MOD}/
+
+%.o: %.f90
+	${F90} ${F90FLAGS} -c $< -o $@
+
+${F90WRAP_SRC}: ${OBJ}
+	${F90WRAP} -m ${PY_MOD} ${WRAPFLAGS} ${F90_SRC}
+
+${SRC_AR}: ${OBJ}
+	ar rcs $@ ${OBJ}
+
+f2py: ${F90WRAP_SRC} ${SRC_AR}
+	CFLAGS="${CFLAGS}" ${F2PY} -c -m _${PY_MOD} ${F2PYFLAGS} f90wrap_*.f90 -L. -lsrc
+
+test: f2py
+	${PYTHON} tests.py
diff --git a/examples/issue373_optional_constructor/Makefile.meson b/examples/issue373_optional_constructor/Makefile.meson
new file mode 100644
index 00000000..b2ee9928
--- /dev/null
+++ b/examples/issue373_optional_constructor/Makefile.meson
@@ -0,0 +1,6 @@
+include ../make.meson.inc
+
+NAME     := pywrapper
+
+test: build
+	$(PYTHON) tests.py
diff --git a/examples/issue373_optional_constructor/main.f90 b/examples/issue373_optional_constructor/main.f90
new file mode 100644
index 00000000..fba77cf4
--- /dev/null
+++ b/examples/issue373_optional_constructor/main.f90
@@ -0,0 +1,28 @@
+module widget_mod
+    implicit none
+    public
+
+    type :: widget_t
+        real :: x
+        real :: scale
+    end type widget_t
+
+    interface widget_t
+        module procedure widget_init
+    end interface widget_t
+
+contains
+
+    function widget_init(x, scale) result(w)
+        real, intent(in) :: x
+        real, intent(in), optional :: scale
+        type(widget_t) :: w
+        w%x = x
+        if (present(scale)) then
+            w%scale = scale
+        else
+            w%scale = 1.0
+        end if
+    end function widget_init
+
+end module widget_mod
diff --git a/examples/issue373_optional_constructor/tests.py b/examples/issue373_optional_constructor/tests.py
new file mode 100644
index 00000000..b3f81720
--- /dev/null
+++ b/examples/issue373_optional_constructor/tests.py
@@ -0,0 +1,19 @@
+import unittest
+
+from pywrapper import widget_mod
+
+
+class TestOptionalConstructor(unittest.TestCase):
+    def test_constructor_without_optional(self):
+        w = widget_mod.widget_t(3.0)
+        self.assertAlmostEqual(w.x, 3.0)
+        self.assertAlmostEqual(w.scale, 1.0)
+
+    def test_constructor_with_optional(self):
+        w = widget_mod.widget_t(2.0, scale=0.5)
+        self.assertAlmostEqual(w.x, 2.0)
+        self.assertAlmostEqual(w.scale, 0.5)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/f90wrap/directc_cgen/arguments_scalar.py b/f90wrap/directc_cgen/arguments_scalar.py
index 31d3d062..0e8341df 100644
--- a/f90wrap/directc_cgen/arguments_scalar.py
+++ b/f90wrap/directc_cgen/arguments_scalar.py
@@ -102,7 +102,9 @@ def prepare_scalar_argument(gen: 'DirectCGenerator', arg: ft.Argument, intent: s
     if optional:
         gen.write(f"if (py_{arg.name} == Py_None) {{")
         gen.indent()
-        gen.write(f"{arg.name}_val = 0;")
+        # Pass a NULL pointer so the Fortran side sees present(arg) == .false.
+        # instead of an argument whose value happens to be zero.
+        gen.write(f"{arg.name} = NULL;")
         gen.dedent()
         gen.write("} else {")
         gen.indent()
@@ -121,7 +123,11 @@ def _prepare_character_none_case(
     """Handle None value for character arguments."""
     gen.write(f"if (py_{arg.name} == Py_None) {{")
     gen.indent()
-    if optional or intent != "in":
+    if optional:
+        # Absent optional argument: pass a NULL pointer so present(arg) == .false.
+        # The output path returns None for a NULL character buffer.
+        gen.write(f"{arg.name} = NULL;")
+    elif intent != "in":
         gen.write(f"{arg.name}_len = {default_len};")
         gen.write(f"if ({arg.name}_len <= 0) {{")
         gen.indent()
diff --git a/f90wrap/directc_cgen/procedures_return.py b/f90wrap/directc_cgen/procedures_return.py
index b7feb475..6f9180f0 100644
--- a/f90wrap/directc_cgen/procedures_return.py
+++ b/f90wrap/directc_cgen/procedures_return.py
@@ -152,7 +152,13 @@ def _prepare_character_output(gen: DirectCGenerator, arg: ft.Argument) -> None:
     if parsed:
         # Check if buffer is from numpy array
         gen.write(f"PyObject* py_{arg.name}_obj = NULL;")
-        gen.write(f"if ({arg.name}_is_array) {{")
+        # An absent optional argument has a NULL buffer: return None for it.
+        gen.write(f"if ({arg.name} == NULL) {{")
+        gen.indent()
+        gen.write("Py_INCREF(Py_None);")
+        gen.write(f"py_{arg.name}_obj = Py_None;")
+        gen.dedent()
+        gen.write(f"}} else if ({arg.name}_is_array) {{")
         gen.indent()
         gen.write("/* Numpy array was modified in place, no return object or free needed */")
         gen.dedent()
diff --git a/f90wrap/transform.py b/f90wrap/transform.py
index 06ad766b..757e56c3 100644
--- a/f90wrap/transform.py
+++ b/f90wrap/transform.py
@@ -554,12 +554,10 @@ def convert_derived_type_arguments(tree, init_lines, sizeof_fortran_t):
         if 'constructor' in sub.attributes:
             # Put the return value of the fortran constructors at first position in the arguments list
             if 'fortranconstructor' in sub.attributes:
-                j = -1
-                for i, arg in enumerate(sub.arguments):
-                    if 'optional' in arg.attributes:
-                        j = i
-                        break
-                assert(sub.arguments[j].name[:4]=='ret_')
+                j = next((i for i, arg in enumerate(sub.arguments)
+                          if arg.name.startswith('ret_')), None)
+                assert j is not None, \
+                    'no ret_ argument found in constructor %s' % sub.name
                 sub.arguments.insert(0, sub.arguments.pop(j))
             sub.arguments[0].attributes = set_intent(sub.arguments[0].attributes, 'intent(out)')