diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0e8f637..ed6e6dd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -43,6 +43,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Building the C library on macOS no longer calls `nproc`. `make -j` uses
+  `sysctl -n hw.ncpu`, then `getconf _NPROCESSORS_ONLN`, then 1 (#95).
 - The source-build installer copies the FFI library under the platform-specific name used
   by the FFI resolver, so successful fallback builds can be found (#71).
 - `BinaryDownloader::download()` no longer calls `curl_close()`, which is a no-op since PHP 8.0
diff --git a/src/Builder.php b/src/Builder.php
index 7fa2e7b..814fabd 100644
--- a/src/Builder.php
+++ b/src/Builder.php
@@ -61,9 +61,9 @@ public function build(): string
             throw BuildException::cmakeFailed($cmakeExitCode);
         }
 
-        // Run make (single invocation; exit code only)
+        // macOS has no GNU nproc binary. sysctl is the Darwin count; getconf covers the rest.
         $makeCmd = sprintf(
-            'cd %s && make -j$(nproc)',
+            'cd %s && make -j"$(sysctl -n hw.ncpu 2>/dev/null || getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1)"',
             escapeshellarg($buildPath)
         );
 
diff --git a/tests/make-jobs-darwin.test.sh b/tests/make-jobs-darwin.test.sh
new file mode 100644
index 0000000..b3c2c7e
--- /dev/null
+++ b/tests/make-jobs-darwin.test.sh
@@ -0,0 +1,32 @@
+#!/bin/bash
+# Builder.php must not ask make for $(nproc). macOS does not ship nproc.
+set -euo pipefail
+root=$(cd "$(dirname "$0")/.." && pwd)
+builder="$root/src/Builder.php"
+
+# The single quotes are the point: this is a source search, not a command.
+# shellcheck disable=SC2016
+if grep -q '$(nproc)' "$builder"; then
+  echo "Builder.php still calls nproc" >&2
+  exit 1
+fi
+
+work=$(mktemp -d)
+set +e
+nproc >"$work/red.out" 2>"$work/red.err"
+red=$?
+set -e
+if [ "$red" -eq 0 ]; then
+  echo "nproc unexpectedly succeeded" >&2
+  exit 1
+fi
+if ! grep -q "command not found" "$work/red.err"; then
+  echo "expected nproc command not found" >&2
+  cat "$work/red.err" >&2
+  exit 1
+fi
+
+jobs=$(sysctl -n hw.ncpu 2>/dev/null || getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1)
+printf '%s\n' "$jobs" | grep -Eq '^[1-9][0-9]*$'
+echo "make jobs darwin ok (nproc exit $red, jobs $jobs)"
+rm -rf "$work"