diff --git a/src/rtlmeter/context.py b/src/rtlmeter/context.py
index 7c2f55c..5cedfe1 100644
--- a/src/rtlmeter/context.py
+++ b/src/rtlmeter/context.py
@@ -14,6 +14,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
+import multiprocessing
 import os
 import time
 from functools import cached_property
@@ -77,10 +78,12 @@ def availableCases(self) -> List[str]:
                     value.append(f"{designName}:{configName}:{testName}")
         return sorted(value)
 
-    # CPUs usable by this process
+    # Number of logical processors usable by this process
     @cached_property
-    def usableCpus(self) -> List[int]:
-        return sorted(_ for _ in os.sched_getaffinity(0))
+    def nProc(self) -> int:
+        if hasattr(os, "sched_getaffinity"):
+            return len(os.sched_getaffinity(0))
+        return multiprocessing.cpu_count()
 
     # Set deadline to now + 'timeout' minutes
     def setTimeout(self, timeout: Optional[int]) -> None:
diff --git a/src/rtlmeter/runcmd.py b/src/rtlmeter/runcmd.py
index 8677da2..b3cdb7b 100644
--- a/src/rtlmeter/runcmd.py
+++ b/src/rtlmeter/runcmd.py
@@ -19,6 +19,7 @@
 import shlex
 import stat
 import subprocess
+import sys
 import time
 from typing import Dict, Final, List
 
@@ -34,6 +35,11 @@
 """
 
 
+TIME_CMD = "time"
+if sys.platform == "darwin":
+    TIME_CMD = "gtime"  # On macOS use GNU time
+
+
 def runcmd(
     cmd: List[str],  # Command + arguments
     tag: str,  # Tag string to use for log and marker files
@@ -67,7 +73,7 @@ def runcmd(
 
     # Actual command line to run, using the cmd file
     timeFile = os.path.join(tagDir, "time.json")
-    cmd = ["time", "-o", timeFile, "-f", _TIMEFORMAT, cmdFileName]
+    cmd = [TIME_CMD, "-o", timeFile, "-f", _TIMEFORMAT, cmdFileName]
 
     # Apply timeout if a deadline is set
     if (timeout := CTX.timeout()) is not None:
diff --git a/src/rtlmeter/verilator.py b/src/rtlmeter/verilator.py
index 22bd895..26e7646 100644
--- a/src/rtlmeter/verilator.py
+++ b/src/rtlmeter/verilator.py
@@ -103,7 +103,7 @@ def job() -> bool:
         cmd = [
             "make",
             "-j",
-            str(len(CTX.usableCpus)),
+            str(CTX.nProc),
             "-C",
             "obj_dir",
             "-f",