diff --git a/kernel/process.c b/kernel/process.c
index c130c55e..2ef74a0d 100644
--- a/kernel/process.c
+++ b/kernel/process.c
@@ -1498,6 +1498,14 @@ int add_process_memory_range(struct process_vm *vm,
 	INIT_LIST_HEAD(&range->tofu_stag_list);
 #endif
 
+	rc = vm_range_insert(vm, range);
+	if (rc) {
+		kprintf("%s: ERROR: could not insert range: %d\n",
+			__func__, rc);
+		kfree(range);
+		return rc;
+	}
+
 	rc = 0;
 	if (phys == NOPHYS) {
 		/* Nothing to map */
@@ -1523,17 +1531,12 @@ int add_process_memory_range(struct process_vm *vm,
 
 	if (rc != 0) {
 		kprintf("%s: ERROR: preparing page tables\n", __FUNCTION__);
+		remove_process_memory_range(vm,
+				range->start, range->end, NULL);
 		kfree(range);
 		return rc;
 	}
 
-	rc = vm_range_insert(vm, range);
-	if (rc) {
-		kprintf("%s: ERROR: could not insert range: %d\n",
-			__FUNCTION__, rc);
-		return rc;
-	}
-
 	/* Clear content! */
 	if (phys != NOPHYS && !(flag & (VR_REMOTE | VR_DEMAND_PAGING))
 			&& ((flag & VR_PROT_MASK) != VR_PROT_NONE)) {
@@ -2739,6 +2742,7 @@ unsigned long extend_process_region(struct process_vm *vm,
 	int rc;
 	size_t len;
 	int npages;
+	struct vm_range *range;
 
 	size_t align_size = vm->proc->heap_extension > PAGE_SIZE ?
 		LARGE_PAGE_SIZE : PAGE_SIZE;
@@ -2755,6 +2759,15 @@ unsigned long extend_process_region(struct process_vm *vm,
 				(align_size - 1)) & align_mask;
 	}
 
+	/* Check if the range to be extended already exists */
+	range = lookup_process_memory_range(vm,
+			end_allocated, new_end_allocated);
+	if (range) {
+		dkprintf("%s: warning: vm_range for extension already exists\n",
+				__func__);
+		return end_allocated;
+	}
+
 	len = new_end_allocated - end_allocated;
 	npages = len >> PAGE_SHIFT;
 
@@ -2782,7 +2795,7 @@ unsigned long extend_process_region(struct process_vm *vm,
 	if ((rc = add_process_memory_range(vm, end_allocated, new_end_allocated,
 					(p == 0 ? 0 : virt_to_phys(p)), flag, NULL, 0,
 					align_shift, NULL)) != 0) {
-		ihk_mc_free_pages_user(p, (new_end_allocated - end_allocated) >> PAGE_SHIFT);
+		ihk_mc_free_pages_user(p, npages);
 		return end_allocated;
 	}
 	// memory_stat_rss_add() is called in add_process_memory_range()
diff --git a/kernel/syscall.c b/kernel/syscall.c
index 4831478c..6e72960e 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -2735,7 +2735,7 @@ SYSCALL_DECLARE(brk)
 	}
 
 	/* If already allocated, just expand and return */
-	if (address < region->brk_end_allocated) {
+	if (address <= region->brk_end_allocated) {
 		region->brk_end = address;
 		r = region->brk_end;
 		goto out;
diff --git a/test/issues/1512/C1512.sh b/test/issues/1512/C1512.sh
new file mode 100755
index 00000000..f31db9ed
--- /dev/null
+++ b/test/issues/1512/C1512.sh
@@ -0,0 +1,60 @@
+#/bin/sh
+
+USELTP=1
+USEOSTEST=0
+
+. ../../common.sh
+
+issue="1512"
+tid=01
+arch=`uname -p`
+
+tname=`printf "C${issue}T%02d" ${tid}`
+echo "*** ${tname} start *******************************"
+tp="shmt09"
+fail_flag=0
+for rep in `seq 1 10`
+do
+	sudo $MCEXEC $LTPBIN/$tp 2>&1 > $tp.txt
+	ok=`grep PASS $tp.txt | wc -l`
+	ng=`grep FAIL $tp.txt | wc -l`
+	echo "shmt09 rep $rep done. (ok=$ok ng=$ng)"
+	if [ $ng -ne 0 ]; then
+		if [ "${arch}" == "x86_64" ]; then
+			echo "OK: Expected fail on ${arch}"
+		else
+			echo "NG: Unexpected fail on ${arch}"
+			fail_flag=1
+		fi
+	else
+		echo "OK: shmt09 PASS"
+	fi
+done
+if [ ${fail_flag} -eq 0 ]; then
+	echo "*** ${tname} PASSED"
+else
+	echo "*** ${tname} FAILED"
+fi
+echo ""
+let tid++
+
+while read tp
+do
+	tname=`printf "C${issue}T%02d" ${tid}`
+	echo "*** ${tname} start *******************************"
+	args=""
+	if [ "$tp" == "mmapstress06" ]; then
+		args="1"
+	fi
+	sudo $MCEXEC $LTPBIN/$tp $args 2>&1 | tee $tp.txt
+	ok=`grep PASS $tp.txt | wc -l`
+	ng=`grep FAIL $tp.txt | wc -l`
+	if [ $ng = 0 ]; then
+		echo "*** ${tname} PASSED ($ok)"
+	else
+		echo "*** ${tname} FAILED (ok=$ok ng=$ng)"
+	fi
+	let tid++
+	echo ""
+done < ./ltp_list
+
diff --git a/test/issues/1512/Makefile b/test/issues/1512/Makefile
new file mode 100644
index 00000000..c5d80af8
--- /dev/null
+++ b/test/issues/1512/Makefile
@@ -0,0 +1,11 @@
+CFLAGS=-g
+LDFLAGS=
+
+TARGET=
+
+all: $(TARGET)
+
+test: all
+	./C1512.sh
+clean:
+	rm -f $(TARGET) *.o *.txt
diff --git a/test/issues/1512/README b/test/issues/1512/README
new file mode 100644
index 00000000..32b433f9
--- /dev/null
+++ b/test/issues/1512/README
@@ -0,0 +1,21 @@
+【Issue#1512 動作確認】
+□ テスト内容
+1. shmt09 を10回連続で実行し、それぞれのプログラムが終了することを確認する
+ なお、x86_64 アーキテクチャではMcKernelのbrk位置をshrinkさせない仕様により、
+ テスト動作が変わり、shmt09はFAILとなる
+
+2. sbrk()を利用する以下のLTPを用いて既存のbrk機能に影響が無いことを確認
+  - sbrk01,02
+  - mmapstress02,05,06
+
+□ 実行手順
+$ make test
+
+McKernelのインストール先や、OSTEST, LTPの配置場所は、
+$HOME/.mck_test_config を参照している
+.mck_test_config は、McKernelをビルドした際に生成されるmck_test_config.sample ファイルを
+$HOMEにコピーし、適宜編集する
+
+□ 実行結果
+x86_64_result.log aarch64_result.log 参照。
+すべての項目をPASSしていることを確認。
diff --git a/test/issues/1512/aarch64_result.log b/test/issues/1512/aarch64_result.log
new file mode 100644
index 00000000..a0e5b28f
--- /dev/null
+++ b/test/issues/1512/aarch64_result.log
@@ -0,0 +1,50 @@
+./C1512.sh
+mcstop+release.sh ... done
+mcreboot.sh -c 37-43,49-55 -m 2G@2,2G@3 -r 37-43:36+49-55:48 -O ... done
+*** C1512T01 start *******************************
+shmt09 rep 1 done. (ok=4 ng=0)
+OK: shmt09 PASS
+shmt09 rep 2 done. (ok=4 ng=0)
+OK: shmt09 PASS
+shmt09 rep 3 done. (ok=4 ng=0)
+OK: shmt09 PASS
+shmt09 rep 4 done. (ok=4 ng=0)
+OK: shmt09 PASS
+shmt09 rep 5 done. (ok=4 ng=0)
+OK: shmt09 PASS
+shmt09 rep 6 done. (ok=4 ng=0)
+OK: shmt09 PASS
+shmt09 rep 7 done. (ok=4 ng=0)
+OK: shmt09 PASS
+shmt09 rep 8 done. (ok=4 ng=0)
+OK: shmt09 PASS
+shmt09 rep 9 done. (ok=4 ng=0)
+OK: shmt09 PASS
+shmt09 rep 10 done. (ok=4 ng=0)
+OK: shmt09 PASS
+*** C1512T01 PASSED
+
+*** C1512T02 start *******************************
+sbrk01      1  TPASS  :  sbrk - Increase by 8192 bytes returned 0x20030000
+sbrk01      2  TPASS  :  sbrk - Increase by -8192 bytes returned 0x20032000
+*** C1512T02 PASSED (2)
+
+*** C1512T03 start *******************************
+sbrk02      0  TINFO  :  setup() bailing inc: 17196646400, ret: 0xffffffffffffffff, sbrk: 0x7fe20030000: errno=ENOMEM(12): Cannot allocate memory
+sbrk02      1  TPASS  :  sbrk(17196646400) failed as expected: TEST_ERRNO=ENOMEM(12): Cannot allocate memory
+*** C1512T03 PASSED (1)
+
+*** C1512T04 start *******************************
+mmapstress02    1  TPASS  :  Test passed
+
+*** C1512T04 PASSED (1)
+
+*** C1512T05 start *******************************
+mmapstress05    1  TPASS  :  Test passed
+
+*** C1512T05 PASSED (1)
+
+*** C1512T06 start *******************************
+mmapstress06    1  TPASS  :  Test passed
+
+*** C1512T06 PASSED (1)
diff --git a/test/issues/1512/ltp_list b/test/issues/1512/ltp_list
new file mode 100644
index 00000000..c678c88e
--- /dev/null
+++ b/test/issues/1512/ltp_list
@@ -0,0 +1,5 @@
+sbrk01
+sbrk02
+mmapstress02
+mmapstress05
+mmapstress06
diff --git a/test/issues/1512/x86_64_result.log b/test/issues/1512/x86_64_result.log
new file mode 100644
index 00000000..c2e31887
--- /dev/null
+++ b/test/issues/1512/x86_64_result.log
@@ -0,0 +1,50 @@
+./C1512.sh
+mcstop+release.sh ... done
+mcreboot.sh -c 1-7,9-15,17-23,25-31 -m 10G@0,10G@1 -r 1-7:0+9-15:8+17-23:16+25-31:24 -O ... done
+*** C1512T01 start *******************************
+shmt09 rep 1 done. (ok=3 ng=1)
+OK: Expected fail on x86_64
+shmt09 rep 2 done. (ok=3 ng=1)
+OK: Expected fail on x86_64
+shmt09 rep 3 done. (ok=3 ng=1)
+OK: Expected fail on x86_64
+shmt09 rep 4 done. (ok=3 ng=1)
+OK: Expected fail on x86_64
+shmt09 rep 5 done. (ok=3 ng=1)
+OK: Expected fail on x86_64
+shmt09 rep 6 done. (ok=3 ng=1)
+OK: Expected fail on x86_64
+shmt09 rep 7 done. (ok=3 ng=1)
+OK: Expected fail on x86_64
+shmt09 rep 8 done. (ok=3 ng=1)
+OK: Expected fail on x86_64
+shmt09 rep 9 done. (ok=3 ng=1)
+OK: Expected fail on x86_64
+shmt09 rep 10 done. (ok=3 ng=1)
+OK: Expected fail on x86_64
+*** C1512T01 PASSED
+
+*** C1512T02 start *******************************
+sbrk01      1  TPASS  :  sbrk - Increase by 8192 bytes returned 0x821000
+sbrk01      2  TPASS  :  sbrk - Increase by -8192 bytes returned 0x823000
+*** C1512T02 PASSED (2)
+
+*** C1512T03 start *******************************
+sbrk02      0  TINFO  :  setup() bailing inc: 28068282368, ret: 0xffffffffffffffff, sbrk: 0x1550dc821000: errno=ENOMEM(12): Cannot allocate memory
+sbrk02      1  TPASS  :  sbrk(28068282368) failed as expected: TEST_ERRNO=ENOMEM(12): Cannot allocate memory
+*** C1512T03 PASSED (1)
+
+*** C1512T04 start *******************************
+mmapstress02    1  TPASS  :  Test passed
+
+*** C1512T04 PASSED (1)
+
+*** C1512T05 start *******************************
+mmapstress05    1  TPASS  :  Test passed
+
+*** C1512T05 PASSED (1)
+
+*** C1512T06 start *******************************
+mmapstress06    1  TPASS  :  Test passed
+
+*** C1512T06 PASSED (1)