diff --git a/llvm/utils/lit/lit/TestRunner.py b/llvm/utils/lit/lit/TestRunner.py
index 4a9b3c618e4f3..76beebd757a75 100644
--- a/llvm/utils/lit/lit/TestRunner.py
+++ b/llvm/utils/lit/lit/TestRunner.py
@@ -600,20 +600,31 @@ def executeBuiltinUmask(cmd, shenv):
 
 def executeBuiltinUlimit(cmd, shenv):
     """executeBuiltinUlimit - Change the current limits."""
-    if os.name != "posix":
+    try:
+        # Try importing the resource module (available on POSIX systems) and
+        # emit an error where it does not exist (e.g., Windows).
+        import resource
+    except ImportError:
         raise InternalShellError(cmd, "'ulimit' not supported on this system")
     if len(cmd.args) != 3:
         raise InternalShellError(cmd, "'ulimit' requires two arguments")
     try:
-        new_limit = int(cmd.args[2])
+        if cmd.args[2] == "unlimited":
+            new_limit = resource.RLIM_INFINITY
+        else:
+            new_limit = int(cmd.args[2])
     except ValueError as err:
         raise InternalShellError(cmd, "Error: 'ulimit': %s" % str(err))
     if cmd.args[1] == "-v":
-        shenv.ulimit["RLIMIT_AS"] = new_limit * 1024
+        if new_limit != resource.RLIM_INFINITY:
+            new_limit = new_limit * 1024
+        shenv.ulimit["RLIMIT_AS"] = new_limit
     elif cmd.args[1] == "-n":
         shenv.ulimit["RLIMIT_NOFILE"] = new_limit
     elif cmd.args[1] == "-s":
-        shenv.ulimit["RLIMIT_STACK"] = new_limit * 1024
+        if new_limit != resource.RLIM_INFINITY:
+            new_limit = new_limit * 1024
+        shenv.ulimit["RLIMIT_STACK"] = new_limit
     elif cmd.args[1] == "-f":
         shenv.ulimit["RLIMIT_FSIZE"] = new_limit
     else:
diff --git a/llvm/utils/lit/tests/Inputs/shtest-ulimit/ulimit_unlimited.txt b/llvm/utils/lit/tests/Inputs/shtest-ulimit/ulimit_unlimited.txt
new file mode 100644
index 0000000000000..b8aa3d5071712
--- /dev/null
+++ b/llvm/utils/lit/tests/Inputs/shtest-ulimit/ulimit_unlimited.txt
@@ -0,0 +1,6 @@
+# RUN: ulimit -f 5
+# RUN: %{python} %S/print_limits.py
+# RUN: ulimit -f unlimited
+# RUN: %{python} %S/print_limits.py
+# Fail the test so that we can assert on the output.
+# RUN: not echo return
diff --git a/llvm/utils/lit/tests/shtest-ulimit.py b/llvm/utils/lit/tests/shtest-ulimit.py
index 21e5a5e2491d1..e15e190920308 100644
--- a/llvm/utils/lit/tests/shtest-ulimit.py
+++ b/llvm/utils/lit/tests/shtest-ulimit.py
@@ -11,7 +11,7 @@
 # RUN: not %{lit} -a -v %{inputs}/shtest-ulimit --order=lexical \
 # RUN:   | FileCheck -DBASE_NOFILE_LIMIT=%{readfile:%t.nofile_limit} %s
 
-# CHECK: -- Testing: 3 tests{{.*}}
+# CHECK: -- Testing: 4 tests{{.*}}
 
 # CHECK-LABEL: FAIL: shtest-ulimit :: ulimit-bad-arg.txt ({{[^)]*}})
 # CHECK: ulimit -n
@@ -25,3 +25,9 @@
 
 # CHECK-LABEL: FAIL: shtest-ulimit :: ulimit_reset.txt ({{[^)]*}})
 # CHECK: RLIMIT_NOFILE=[[BASE_NOFILE_LIMIT]]
+
+# CHECK-LABEL: FAIL: shtest-ulimit :: ulimit_unlimited.txt ({{[^)]*}})
+# CHECK: ulimit -f 5
+# CHECK: RLIMIT_FSIZE=5
+# CHECK: ulimit -f unlimited
+# CHECK: RLIMIT_FSIZE=-1