diff --git a/Lib/tkinter/simpledialog.py b/Lib/tkinter/simpledialog.py
index 885804b..45302b4 100644
--- a/Lib/tkinter/simpledialog.py
+++ b/Lib/tkinter/simpledialog.py
@@ -282,7 +282,7 @@
         self.entry = Entry(master, name="entry")
         self.entry.grid(row=1, padx=5, sticky=W+E)
 
-        if self.initialvalue:
+        if self.initialvalue is not None:
             self.entry.insert(0, self.initialvalue)
             self.entry.select_range(0, END)
 
diff --git a/Misc/ACKS b/Misc/ACKS
index e04677e..1a094a1 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -633,6 +633,7 @@
 Mike Meyer
 Steven Miale
 Trent Mick
+Tom Middleton
 Stan Mihai
 Stefan Mihaila
 Aristotelis Mikropoulos
diff --git a/Misc/NEWS b/Misc/NEWS
index 5ede324..454a70c 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -98,6 +98,9 @@
 Library
 -------
 
+- Issue #12288: Consider '0' and '0.0' as valid initialvalue
+  for tkinter SimpleDialog.
+
 - Issue #15489: Add a __sizeof__ implementation for BytesIO objects.
   Patch by Serhiy Storchaka.