diff --git a/Lib/test/test_array.py b/Lib/test/test_array.py
index ba9c25c835bc39..943420f4c3f4e8 100755
--- a/Lib/test/test_array.py
+++ b/Lib/test/test_array.py
@@ -1612,6 +1612,13 @@ def test_overflows(self):
         self.assertRaises(OverflowError, array.array, self.typecode, [123456])
         # Overflows also float type:
         self.assertRaises(OverflowError, array.array, self.typecode, [1e300])
+        # A failed append, insert or extend leaves the array unchanged:
+        for x in 123456, 1e300:
+            a = array.array(self.typecode, [1])
+            self.assertRaises(OverflowError, a.append, x)
+            self.assertRaises(OverflowError, a.insert, 0, x)
+            self.assertRaises(OverflowError, a.extend, [x])
+            self.assertEqual(a, array.array(self.typecode, [1]))
 
 class FloatTest(FPTest, unittest.TestCase):
     typecode = 'f'
@@ -1619,6 +1626,12 @@ class FloatTest(FPTest, unittest.TestCase):
 
     def test_overflows(self):
         self.assertRaises(OverflowError, array.array, self.typecode, [1e300])
+        # A failed append, insert or extend leaves the array unchanged:
+        a = array.array(self.typecode, [1])
+        self.assertRaises(OverflowError, a.append, 1e300)
+        self.assertRaises(OverflowError, a.insert, 0, 1e300)
+        self.assertRaises(OverflowError, a.extend, [1e300])
+        self.assertEqual(a, array.array(self.typecode, [1]))
 
 class DoubleTest(FPTest, unittest.TestCase):
     typecode = 'd'
@@ -1649,6 +1662,13 @@ class ComplexFloatTest(CFPTest, unittest.TestCase):
     def test_overflows(self):
         self.assertRaises(OverflowError, array.array, self.typecode, [1e300])
         self.assertRaises(OverflowError, array.array, self.typecode, [1e300j])
+        # A failed append, insert or extend leaves the array unchanged:
+        for x in 1e300, 1e300j:
+            a = array.array(self.typecode, [1])
+            self.assertRaises(OverflowError, a.append, x)
+            self.assertRaises(OverflowError, a.insert, 0, x)
+            self.assertRaises(OverflowError, a.extend, [x])
+            self.assertEqual(a, array.array(self.typecode, [1]))
 
 class ComplexDoubleTest(CFPTest, unittest.TestCase):
     typecode = 'Zd'
diff --git a/Misc/NEWS.d/next/Library/2026-09-28-13-52-36.gh-issue-158345.GNlDCF.rst b/Misc/NEWS.d/next/Library/2026-09-28-13-52-36.gh-issue-158345.GNlDCF.rst
new file mode 100644
index 00000000000000..208b3e8055e54a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-09-28-13-52-36.gh-issue-158345.GNlDCF.rst
@@ -0,0 +1,3 @@
+Fix :meth:`array.array.append`, :meth:`~array.array.insert` and
+:meth:`~array.array.extend` leaving an extra item in the array when they
+raise :exc:`OverflowError` for the ``'e'``, ``'f'`` or ``'Zf'`` type code.
diff --git a/Modules/arraymodule.c b/Modules/arraymodule.c
index ef492d143d5644..fee9ba3d6debf2 100644
--- a/Modules/arraymodule.c
+++ b/Modules/arraymodule.c
@@ -823,6 +823,8 @@ getarrayitem(PyObject *op, Py_ssize_t i)
     return (*ap->ob_descr->getitem)(ap, i);
 }
 
+static int array_del_slice(arrayobject *a, Py_ssize_t ilow, Py_ssize_t ihigh);
+
 static int
 ins1(arrayobject *self, Py_ssize_t where, PyObject *v)
 {
@@ -832,8 +834,6 @@ ins1(arrayobject *self, Py_ssize_t where, PyObject *v)
         PyErr_BadInternalCall();
         return -1;
     }
-    if ((*self->ob_descr->setitem)(self, -1, v) < 0)
-        return -1;
 
     if (array_resize(self, n+1) == -1)
         return -1;
@@ -850,7 +850,11 @@ ins1(arrayobject *self, Py_ssize_t where, PyObject *v)
         memmove(items + (where+1)*self->ob_descr->itemsize,
             items + where*self->ob_descr->itemsize,
             (n-where)*self->ob_descr->itemsize);
-    return (*self->ob_descr->setitem)(self, where, v);
+    if ((*self->ob_descr->setitem)(self, where, v) < 0) {
+        array_del_slice(self, where, where+1);
+        return -1;
+    }
+    return 0;
 }
 
 /* Methods */