diff --git a/samples/net/common/Makefile.ipstack b/samples/net/common/Makefile.ipstack
index 2baaaa877b2..81aef24de3c 100644
--- a/samples/net/common/Makefile.ipstack
+++ b/samples/net/common/Makefile.ipstack
@@ -18,7 +18,7 @@ ifdef QEMU_NUM
 	QEMU_EXTRA_FLAGS += -serial none -serial pipe:${PIPE_BASE}-${QEMU_NUM}	\
 			    -pidfile qemu-${QEMU_NUM}.pid
 else
-	QEMU_EXTRA_FLAGS += -serial none -serial unix:/tmp/slip.sock
+	QEMU_EXTRA_FLAGS += -serial none -serial unix:/tmp/slip.sock$(QEMU_INSTANCE)
 endif
 
 PIPE_SERVER_IN=${PIPE_BASE}-server.in
diff --git a/scripts/Makefile.qemu b/scripts/Makefile.qemu
index 2e21807c2a4..b0bba796b34 100644
--- a/scripts/Makefile.qemu
+++ b/scripts/Makefile.qemu
@@ -6,7 +6,7 @@
 
 # Abstraction of 'run' goal with Qemu
 
-QEMU_FLAGS = $(QEMU_FLAGS_$(ARCH)) -pidfile qemu.pid
+QEMU_FLAGS = $(QEMU_FLAGS_$(ARCH)) -pidfile qemu$(QEMU_INSTANCE).pid
 
 ifneq ($(QEMU_PTY),)
     QEMU_FLAGS += -serial pty