diff --git a/pandas/core/reshape/reshape.py b/pandas/core/reshape/reshape.py
index eaeb4a50d0bf3..7e27c924bfbed 100644
--- a/pandas/core/reshape/reshape.py
+++ b/pandas/core/reshape/reshape.py
@@ -747,7 +747,18 @@ def _convert_level_number(level_num: int, columns: Index):
         if slice_len != levsize:
             chunk = this.loc[:, this.columns[loc]]
             chunk.columns = level_vals_nan.take(chunk.columns.codes[-1])
-            value_slice = chunk.reindex(columns=level_vals_used).values
+            # Override fill value to prevent upcasting to float64
+            # if we have lower precision floats
+            common_type = find_common_type(chunk.dtypes.tolist())
+            if np.issubdtype(common_type, np.floating):
+                fill_value = common_type.type(np.nan)
+            elif is_extension_array_dtype(common_type):
+                fill_value = common_type.na_value
+            else:
+                fill_value = np.nan
+            value_slice = chunk.reindex(
+                columns=level_vals_used, fill_value=fill_value
+            ).values
         else:
             subset = this.iloc[:, loc]
             dtype = find_common_type(subset.dtypes.tolist())
diff --git a/pandas/tests/frame/test_stack_unstack.py b/pandas/tests/frame/test_stack_unstack.py
index 889c44522f7bb..98cc8871d4d28 100644
--- a/pandas/tests/frame/test_stack_unstack.py
+++ b/pandas/tests/frame/test_stack_unstack.py
@@ -1481,6 +1481,19 @@ def test_stack(self, multiindex_year_month_day_dataframe_random_data):
         expected = ymd.unstack(0).stack(0)
         tm.assert_equal(result, expected)
 
+    def test_stack_nans_doesnt_upcast_float(self):
+        # GH 51059
+        df = DataFrame({("n1", "q1"): [1], ("n2", "q2"): [2]}, dtype="float32")
+        res = df.stack(level=0)
+        exp = DataFrame(
+            {
+                "q1": np.array([1.0, np.nan], dtype="float32"),
+                "q2": np.array([np.nan, 2.0], dtype="float32"),
+            },
+            index=MultiIndex.from_product([[0], ["n1", "n2"]]),
+        )
+        tm.assert_frame_equal(res, exp)
+
     @pytest.mark.parametrize(
         "idx, columns, exp_idx",
         [