diff --git a/src/os/exec_test.go b/src/os/exec_test.go
index b49dd0dd914..07a06ec0ff3 100644
--- a/src/os/exec_test.go
+++ b/src/os/exec_test.go
@@ -6,7 +6,6 @@ package os_test
 
 import (
 	"internal/testenv"
-	"math"
 	"os"
 	"os/signal"
 	"runtime"
@@ -76,28 +75,3 @@ func TestProcessReleaseTwice(t *testing.T) {
 		t.Fatalf("second Release: got err %v, want %v", err, want)
 	}
 }
-
-// Lookup of a process that does not exist at time of lookup.
-func TestProcessAlreadyDone(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("Windows does not support lookup of non-existant process")
-	}
-	if runtime.GOARCH == "wasm" {
-		t.Skip("Wait not supported om wasm port")
-	}
-
-	// Theoretically MaxInt32 is a valid PID, but the chance of it actually
-	// being used is extremely unlikely.
-	p, err := os.FindProcess(math.MaxInt32)
-	if err != nil {
-		t.Fatalf("FindProcess(math.MaxInt32) got err %v, want nil", err)
-	}
-
-	if ps, err := p.Wait(); err != os.ErrProcessDone {
-		t.Errorf("Wait() got err %v (ps %+v), want ErrProcessDone", err, ps)
-	}
-
-	if err := p.Release(); err != nil {
-		t.Errorf("Release() got err %v, want nil", err)
-	}
-}
diff --git a/src/os/exec_unix_test.go b/src/os/exec_unix_test.go
index 69bcdbdad18..81d8e1cfee6 100644
--- a/src/os/exec_unix_test.go
+++ b/src/os/exec_unix_test.go
@@ -7,8 +7,11 @@
 package os_test
 
 import (
+	"errors"
 	"internal/testenv"
+	"math"
 	. "os"
+	"runtime"
 	"syscall"
 	"testing"
 )
@@ -27,6 +30,33 @@ func TestErrProcessDone(t *testing.T) {
 	}
 }
 
+// Lookup of a process that does not exist at time of lookup.
+func TestProcessAlreadyDone(t *testing.T) {
+	// Theoretically MaxInt32 is a valid PID, but the chance of it actually
+	// being used is extremely unlikely.
+	pid := math.MaxInt32
+	if runtime.GOOS == "solaris" || runtime.GOOS == "illumos" {
+		// Solaris/Illumos have a lower limit, above which wait returns
+		// EINVAL (see waitid in usr/src/uts/common/os/exit.c in
+		// illumos). This is configurable via sysconf(_SC_MAXPID), but
+		// we'll just take the default.
+		pid = 30000-1
+	}
+
+	p, err := FindProcess(pid)
+	if err != nil {
+		t.Fatalf("FindProcess(math.MaxInt32) got err %v, want nil", err)
+	}
+
+	if ps, err := p.Wait(); !errors.Is(err, syscall.ECHILD) {
+		t.Errorf("Wait() got err %v (ps %+v), want %v", err, ps, syscall.ECHILD)
+	}
+
+	if err := p.Release(); err != nil {
+		t.Errorf("Release() got err %v, want nil", err)
+	}
+}
+
 func TestUNIXProcessAlive(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 	t.Parallel()
diff --git a/src/os/pidfd_linux.go b/src/os/pidfd_linux.go
index c71c366de63..0404c4ff64b 100644
--- a/src/os/pidfd_linux.go
+++ b/src/os/pidfd_linux.go
@@ -74,7 +74,10 @@ func (p *Process) pidfdWait() (*ProcessState, error) {
 	handle, status := p.handleTransientAcquire()
 	switch status {
 	case statusDone:
-		return nil, ErrProcessDone
+		// Process already completed Wait, or was not found by
+		// pidfdFind. Return ECHILD for consistency with what the wait
+		// syscall would return.
+		return nil, NewSyscallError("wait", syscall.ECHILD)
 	case statusReleased:
 		return nil, syscall.EINVAL
 	}
diff --git a/src/os/pidfd_linux_test.go b/src/os/pidfd_linux_test.go
index 2f567eed409..837593706ba 100644
--- a/src/os/pidfd_linux_test.go
+++ b/src/os/pidfd_linux_test.go
@@ -5,8 +5,10 @@
 package os_test
 
 import (
+	"errors"
 	"internal/testenv"
 	"os"
+	"syscall"
 	"testing"
 )
 
@@ -47,7 +49,7 @@ func TestFindProcessViaPidfd(t *testing.T) {
 	if err := proc.Signal(os.Kill); err != os.ErrProcessDone {
 		t.Errorf("Signal: got %v, want %v", err, os.ErrProcessDone)
 	}
-	if _, err := proc.Wait(); err != os.ErrProcessDone {
+	if _, err := proc.Wait(); !errors.Is(err, syscall.ECHILD) {
 		t.Errorf("Wait: got %v, want %v", err, os.ErrProcessDone)
 	}
 	// Release never returns errors on Unix.