diff --git a/ChangeLog b/ChangeLog
index e5fc85e..f232c55 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2025-04-19  Bruno Haible  <bruno@clisp.org>
+
+	Optimize: Make Bool_Array take less memory.
+	Less memory means: less cache misses.
+	This reduces the execution time of gperf on large inputs by ca. 2.5%.
+	* src/bool-array.h (Bool_Array): For the _storage_array and
+	_iteration_number fields, use 'unsigned char' instead of 'unsigned int'.
+	* src/bool-array.icc (Bool_Array::Bool_Array, Bool_Array::clear: Update.
+	* src/bool-array.cc (Bool_Array::~Bool_Array): Update.
+
 2025-04-19  Bruno Haible  <bruno@clisp.org>
 
 	tests: Add unit test with many keywords.
diff --git a/src/bool-array.cc b/src/bool-array.cc
index c181a7a..5998575 100644
--- a/src/bool-array.cc
+++ b/src/bool-array.cc
@@ -35,7 +35,7 @@ Bool_Array::~Bool_Array ()
     fprintf (stderr, "\ndumping boolean array information\n"
              "size = %d\niteration number = %d\nend of array dump\n",
              _size, _iteration_number);
-  delete[] const_cast<unsigned int *>(_storage_array);
+  delete[] const_cast<unsigned char *>(_storage_array);
 }
 
 #ifndef __OPTIMIZE__
diff --git a/src/bool-array.h b/src/bool-array.h
index 6167d38..c62fefa 100644
--- a/src/bool-array.h
+++ b/src/bool-array.h
@@ -2,7 +2,7 @@
 
 /* Simple lookup table abstraction implemented as an Iteration Number Array.
 
-   Copyright (C) 1989-1998, 2002 Free Software Foundation, Inc.
+   Copyright (C) 1989-1998, 2002, 2025 Free Software Foundation, Inc.
    Written by Douglas C. Schmidt <schmidt@ics.uci.edu>
    and Bruno Haible <bruno@clisp.org>.
 
@@ -56,11 +56,11 @@ private:
 
   /* Current iteration number.  Always nonzero.  Starts out as 1, and is
      incremented each time clear() is called.  */
-  unsigned int          _iteration_number;
+  unsigned char         _iteration_number;
 
   /* For each index, we store in storage_array[index] the iteration_number at
      the time set_bit(index) was last called.  */
-  unsigned int * const  _storage_array;
+  unsigned char * const _storage_array;
 };
 
 #ifdef __OPTIMIZE__  /* efficiency hack! */
diff --git a/src/bool-array.icc b/src/bool-array.icc
index e913656..20f8489 100644
--- a/src/bool-array.icc
+++ b/src/bool-array.icc
@@ -1,6 +1,6 @@
 /* Inline Functions for bool-array.{h,cc}.
 
-   Copyright (C) 1989-1998, 2002 Free Software Foundation, Inc.
+   Copyright (C) 1989-1998, 2002, 2025 Free Software Foundation, Inc.
    Written by Douglas C. Schmidt <schmidt@ics.uci.edu>
    and Bruno Haible <bruno@clisp.org>.
 
@@ -30,7 +30,7 @@ INLINE
 Bool_Array::Bool_Array (unsigned int size)
   : _size (size),
     _iteration_number (1),
-    _storage_array (new unsigned int [size])
+    _storage_array (new unsigned char [size])
 {
   memset (_storage_array, 0, size * sizeof (_storage_array[0]));
   if (option[DEBUG])
@@ -60,8 +60,8 @@ INLINE void
 Bool_Array::clear ()
 {
   /* If we wrap around it's time to zero things out again!  However, this only
-     occurs once about every 2^32 iterations, so it will not happen more
-     frequently than once per second.  */
+     occurs once about every 2^8 iterations, so it does not take much time on
+     average.  */
 
   if (++_iteration_number == 0)
     {