diff --git a/Help/command/string.rst b/Help/command/string.rst
index 2c7847acc3793157cc31530d4792309b27cab17e..698a91dcad2c0cd5adf5dea5cfb37d45f0980588 100644
--- a/Help/command/string.rst
+++ b/Help/command/string.rst
@@ -296,6 +296,7 @@ specifiers:
 
 ::
 
+   %%        A literal percent sign (%).
    %d        The day of the current month (01-31).
    %H        The hour on a 24-hour clock (00-23).
    %I        The hour on a 12-hour clock (01-12).
diff --git a/Help/release/dev/timestamp-percent.rst b/Help/release/dev/timestamp-percent.rst
new file mode 100644
index 0000000000000000000000000000000000000000..046d6c507e43f49fab09d29d3e065e0eaaeea271
--- /dev/null
+++ b/Help/release/dev/timestamp-percent.rst
@@ -0,0 +1,5 @@
+timestamp-percent
+-----------------
+
+* The :command:`string(TIMESTAMP)` command learned to treat ``%%``
+  as a way to encode plain ``%``.
diff --git a/Source/cmTimestamp.cxx b/Source/cmTimestamp.cxx
index 1e5ac5b2d0969290ea43de03626e9fbc3ed6b398..3d42e262e2bdbe1c7e31c24e2db20fdcd0cfbc8c 100644
--- a/Source/cmTimestamp.cxx
+++ b/Source/cmTimestamp.cxx
@@ -136,6 +136,7 @@ std::string cmTimestamp::AddTimestampComponent(char flag,
     case 'w':
     case 'y':
     case 'Y':
+    case '%':
       break;
     case 's': // Seconds since UNIX epoch (midnight 1-jan-1970)
     {
diff --git a/Tests/RunCMake/string/Timestamp-stderr.txt b/Tests/RunCMake/string/Timestamp-stderr.txt
index c12b0707e66536b3415f37a724f3cc4a0bf0d040..653974c620a29eac7eea3be674a8fe9269e88fcf 100644
--- a/Tests/RunCMake/string/Timestamp-stderr.txt
+++ b/Tests/RunCMake/string/Timestamp-stderr.txt
@@ -1 +1 @@
-RESULT=2005-08-07 23:19:49 Sun Aug 05 day=219 wd=0 week=32 %%I=11
+RESULT=2005-08-07 23:19:49 Sun Aug 05 day=219 wd=0 week=32 %I=11 epoch=1123456789
diff --git a/Tests/RunCMake/string/Timestamp.cmake b/Tests/RunCMake/string/Timestamp.cmake
index 1232300156bc2b6e8b84598ee98f13627a947dc7..d2420394292941223eb161fdc9e26492b1aa8c3a 100644
--- a/Tests/RunCMake/string/Timestamp.cmake
+++ b/Tests/RunCMake/string/Timestamp.cmake
@@ -1,3 +1,3 @@
 set(ENV{SOURCE_DATE_EPOCH} "1123456789")
-string(TIMESTAMP RESULT "%Y-%m-%d %H:%M:%S %a %b %y day=%j wd=%w week=%U %%I=%I" UTC)
+string(TIMESTAMP RESULT "%Y-%m-%d %H:%M:%S %a %b %y day=%j wd=%w week=%U %%I=%I epoch=%s" UTC)
 message("RESULT=${RESULT}")