diff --git a/autotest/t015_test.py b/autotest/t015_test.py
index 09bed0f128..3164b5e36d 100644
--- a/autotest/t015_test.py
+++ b/autotest/t015_test.py
@@ -32,7 +32,54 @@
 else:
     path = os.path.join("..", "examples", "data", "mf2005_test")
 
-str_items = {0: {"mfnam": "str.nam", "sfrfile": "str.str"}}
+str_items = {
+    0: {
+        "mfnam": "str.nam",
+        "sfrfile": "str.str",
+        "lstfile": "str.lst",
+    }
+}
+
+
+def test_str_issue1164():
+    m = flopy.modflow.Modflow.load(
+        str_items[0]["mfnam"],
+        exe_name=mfexe,
+        model_ws=path,
+        verbose=False,
+        check=False,
+    )
+
+    ws = os.path.join(tpth, "issue-1164")
+    m.change_model_ws(ws)
+
+    # adjust stress period data
+    spd0 = m.str.stress_period_data[0]
+    spd0["flow"][0] = 2.1149856e6  # 450000000000000000.0000e-17
+    m.str.stress_period_data[0] = spd0
+
+    # write model datasets and run fixed
+    m.write_input()
+    success = m.run_model()
+    assert success, "could not run base model"
+
+    # get the budget
+    lst_pth = os.path.join(ws, str_items[0]["lstfile"])
+    base_wb = flopy.utils.MfListBudget(lst_pth).get_dataframes()[0]
+
+    # set the model to free format
+    m.set_ifrefm()
+
+    # write model datasets and run revised
+    m.write_input()
+    success = m.run_model()
+    assert success, "could not run revised model"
+
+    # get the revised budget
+    revised_wb = flopy.utils.MfListBudget(lst_pth).get_dataframes()[0]
+
+    # test if the budgets are the same
+    assert revised_wb.equals(base_wb), "water budgets do not match"
 
 
 def test_str_free():
@@ -43,7 +90,7 @@ def test_str_free():
         verbose=False,
         check=False,
     )
-    ws = tpth
+    ws = os.path.join(tpth, "fixed")
     m.change_model_ws(ws)
 
     # get pointer to str package
@@ -116,7 +163,7 @@ def test_str_free():
     msg = "could not load the fixed format model with aux variables"
     assert m2 is not None, msg
 
-    ws = os.path.join(tpth, "mf2005")
+    ws = os.path.join(tpth, "free")
     m.change_model_ws(ws)
     m.set_ifrefm()
     m.write_input()
@@ -145,7 +192,7 @@ def test_str_free():
     # compare the fixed and free format head files
     if run:
         if pymake is not None:
-            fn1 = os.path.join(tpth, "str.nam")
+            fn1 = os.path.join(tpth, "fixed", "str.nam")
             fn2 = os.path.join(ws, "str.nam")
             success = pymake.compare_heads(fn1, fn2, verbose=True)
             msg = "fixed and free format input output head files are different"
@@ -162,5 +209,6 @@ def test_str_plot():
 
 
 if __name__ == "__main__":
+    test_str_issue1164()
     test_str_free()
     test_str_plot()
diff --git a/flopy/utils/flopy_io.py b/flopy/utils/flopy_io.py
index 4cb074392c..8fd8fdd793 100755
--- a/flopy/utils/flopy_io.py
+++ b/flopy/utils/flopy_io.py
@@ -185,18 +185,25 @@ def write_fixed_var(v, length=10, ipos=None, free=False, comment=None):
         if free:
             write_fmt = "{} "
         else:
+            width = ipos[n]
             if isinstance(v[n], (float, np.float32, np.float64)):
-                width = ipos[n] - 6
-                vmin, vmax = 10 ** -width, 10 ** width
+                decimal = width - 6
+                vmin, vmax = 10 ** -decimal, 10 ** decimal
                 if abs(v[n]) < vmin or abs(v[n]) > vmax:
-                    ctype = "g"
+                    ctype = "g"  # default precision is 6 if not specified
                 else:
-                    ctype = ".{}f".format(width)
+                    ctype = ".{}f".format(decimal)
+                    # evaluate if the fixed format value will exceed width
+                    if (
+                        len("{{:>{}{}}}".format(width, ctype).format(v[n]))
+                        > width
+                    ):
+                        ctype = ".{}g".format(decimal)  # preserve precision
             elif isinstance(v[n], (int, np.int32, np.int64)):
                 ctype = "d"
             else:
                 ctype = ""
-            write_fmt = "{{:>{}{}}}".format(ipos[n], ctype)
+            write_fmt = "{{:>{}{}}}".format(width, ctype)
         out += write_fmt.format(v[n])
     if comment is not None:
         out += "  # {}".format(comment)