diff --git a/Help/command/string.rst b/Help/command/string.rst
index 07d0ff3f2..351385bf1 100644
--- a/Help/command/string.rst
+++ b/Help/command/string.rst
@@ -73,8 +73,13 @@ TOUPPER/TOLOWER will convert string to upper/lower characters.
 
 LENGTH will return a given string's length.
 
-SUBSTRING will return a substring of a given string.  If length is -1
+SUBSTRING will return a substring of a given string. If length is -1
 the remainder of the string starting at begin will be returned.
+If string is shorter than length then end of string is used instead.
+
+.. note::
+  CMake 3.1 and below reported an error if length pointed past
+  the end of string.
 
 STRIP will return a substring of a given string with leading and
 trailing spaces removed.
diff --git a/Source/cmStringCommand.cxx b/Source/cmStringCommand.cxx
index 90a8f8546..ce7c854aa 100644
--- a/Source/cmStringCommand.cxx
+++ b/Source/cmStringCommand.cxx
@@ -711,12 +711,10 @@ bool cmStringCommand::HandleSubstringCommand(std::vector<std::string> const&
     this->SetError(ostr.str());
     return false;
     }
-  int leftOverLength = intStringLength - begin;
-  if ( end < -1 || end > leftOverLength )
+  if ( end < -1 )
     {
     cmOStringStream ostr;
-    ostr << "end index: " << end << " is out of range -1 - "
-         << leftOverLength;
+    ostr << "end index: " << end << " should be -1 or greater";
     this->SetError(ostr.str());
     return false;
     }
diff --git a/Tests/CMakeTests/StringTest.cmake.in b/Tests/CMakeTests/StringTest.cmake.in
index a9fe428e3..92e70c3ac 100644
--- a/Tests/CMakeTests/StringTest.cmake.in
+++ b/Tests/CMakeTests/StringTest.cmake.in
@@ -63,7 +63,7 @@ check_cmake_test(String
 # Execute each test listed in StringTestScript.cmake:
 #
 set(scriptname "@CMAKE_CURRENT_SOURCE_DIR@/StringTestScript.cmake")
-set(number_of_tests_expected 69)
+set(number_of_tests_expected 70)
 
 include("@CMAKE_CURRENT_SOURCE_DIR@/ExecuteScriptTests.cmake")
 execute_all_script_tests(${scriptname} number_of_tests_executed)
@@ -75,6 +75,6 @@ message(STATUS "scriptname='${scriptname}'")
 message(STATUS "number_of_tests_executed='${number_of_tests_executed}'")
 message(STATUS "number_of_tests_expected='${number_of_tests_expected}'")
 
-if(number_of_tests_executed LESS number_of_tests_expected)
+if(NOT number_of_tests_executed EQUAL number_of_tests_expected)
   message(FATAL_ERROR "error: some test cases were skipped")
 endif()
diff --git a/Tests/CMakeTests/StringTestScript.cmake b/Tests/CMakeTests/StringTestScript.cmake
index a562e71d3..44d56531f 100644
--- a/Tests/CMakeTests/StringTestScript.cmake
+++ b/Tests/CMakeTests/StringTestScript.cmake
@@ -122,14 +122,17 @@ elseif(testname STREQUAL substring_not_enough_args) # fail
 elseif(testname STREQUAL substring_begin_too_large) # fail
   string(SUBSTRING "abcdefg" 25 100 v)
 
-elseif(testname STREQUAL substring_end_too_large) # fail
+elseif(testname STREQUAL substring_end_larger_than_strlen) # pass
   string(SUBSTRING "abcdefg" 1 100 v)
 
 elseif(testname STREQUAL substring_begin_less_than_zero) # fail
-  string(SUBSTRING "abcdefg" -2 4 v)
+  string(SUBSTRING "abcdefg" -1 4 v)
 
-elseif(testname STREQUAL substring_end_less_than_begin) # fail
-  string(SUBSTRING "abcdefg" 6 3 v)
+elseif(testname STREQUAL substring_end_less_than_zero) # pass
+  string(SUBSTRING "abcdefg" 0 -1 v)
+
+elseif(testname STREQUAL substring_end_less_than_begin) # pass
+  string(SUBSTRING "abcdefg" 6 0 v)
 
 elseif(testname STREQUAL length_not_enough_args) # fail
   string(LENGTH)