diff --git a/modules/ShString/ShString.c b/modules/ShString/ShString.c
index 6b6b7c5..e21839f 100644
--- a/modules/ShString/ShString.c
+++ b/modules/ShString/ShString.c
@@ -45,26 +45,8 @@ static void ExchangeString(void) {
 	int target = getCaliValue();
 	int pat    = getCaliValue();
 	int patr   = getCaliValue();
-	const char *start = v_str(target -1);
-	const char *next;
-	char dst[STRVAR_LEN] = "";
-	
+	v_strReplaceAll(target - 1, pat - 1, patr - 1);
 	DEBUG_COMMAND("ShString.ExchangeString: %d,%d,%d:\n", target, pat, patr);
-	
-	if (v_strlen(target -1) == 0 || v_strlen(pat -1) == 0) {
-		return;
-	}
-	
-	while(TRUE) {
-		next = strstr(start, v_str(pat -1));
-		if (next == NULL) break;
-		strncat(dst, start, (size_t)(next - start));
-		strncat(dst, v_str(patr -1), sizeof(dst) - strlen(dst));
-		start = next + v_strlen(pat -1);
-	}
-	
-	strncat(dst, start, sizeof(dst) - strlen(dst));
-	v_strcpy(target -1, dst);
 }
 
 static void SetNum16String(void) { /* 1 */
diff --git a/src/variable.c b/src/variable.c
index e67441d..57f24ea 100644
--- a/src/variable.c
+++ b/src/variable.c
@@ -266,6 +266,34 @@ int v_strGetCharType(int no, int pos) {
 	return CHECKSJIS1BYTE(*p) ? 2 : 1;
 }
 
+void v_strReplaceAll(int no, int pattern, int replacement) {
+	const char *pat = v_str(pattern);
+	if (!*pat)
+		return;
+	const char *repl = v_str(replacement);
+
+	if (no < 0 || no >= strvar_cnt) {
+		WARNING("string index out of range: %d", no);
+		return;
+	}
+	if (!strVar[no])
+		return;
+	char *src = strVar[no];
+	strVar[no] = NULL;
+
+	char *start = src, *found;;
+	while ((found = strstr(start, pat))) {
+		char bak = *found;
+		*found = '\0';
+		v_strcat(no, start);
+		*found = bak;
+		v_strcat(no, repl);
+		start = found + strlen(pat);
+	}
+	v_strcat(no, start);
+	free(src);
+}
+
 #ifdef DEBUG
 
 void debug_showvariable() {
diff --git a/src/variable.h b/src/variable.h
index 99a1a54..5bf6a6a 100644
--- a/src/variable.h
+++ b/src/variable.h
@@ -68,5 +68,6 @@ extern void v_strFromVars(int no, const int *vars);
 extern int v_strToVars(int no, int *vars);
 extern const char *v_str(int no);
 extern int v_strGetCharType(int no, int pos);
+extern void v_strReplaceAll(int no, int pattern, int replacement);
 
 #endif /* !__VARIABLE__ */
diff --git a/test/ShString.HEL b/test/ShString.HEL
new file mode 100644
index 0000000..5c27466
--- /dev/null
+++ b/test/ShString.HEL
@@ -0,0 +1,7 @@
+void ExchangeString(IString arg1, IString arg2, IString arg3)
+void SetNum16String(pword arg1, IString arg2)
+void SetNum16HalfString(pword arg1, IString arg2)
+void SetNum32String(pword arg1, IString arg2)
+void SetNum32HalfString(pword arg1, IString arg2)
+void GetArrayString(pword arg1, int arg2, IString arg3)
+void SetWindowTitle(IString arg1, ISys3xSystem arg2)
diff --git a/test/System39.ain b/test/System39.ain
new file mode 100644
index 0000000..ffa45f3
Binary files /dev/null and b/test/System39.ain differ
diff --git a/test/strvar.adv b/test/strvar.adv
index f795b65..3cc17ee 100644
--- a/test/strvar.adv
+++ b/test/strvar.adv
@@ -96,6 +96,7 @@ const word str4 = 13:
 
 	\test_MG7:
 	\test_strFuncs:
+	\test_ShString:
 
 	%0:
 
@@ -153,6 +154,15 @@ const word str4 = 13:
 
 	\0:
 
+*test_ShString:
+	MS str1,"あああああ":
+	MS str2,"ああ":
+	MS str3,"いいい":
+	ShString.ExchangeString str1,str2,str3:
+	MS str4,"いいいいいいあ":
+	~AssertStrEquals str1,str4,__LINE__:
+	\0:
+
 **MPtoString dst,src,len:
 	MG 100,0:
 	MG 1,dst:
diff --git a/test/test.hed b/test/test.hed
index 67cc26a..5797f33 100644
--- a/test/test.hed
+++ b/test/test.hed
@@ -3,3 +3,6 @@ test.adv
 util.adv
 array.adv
 strvar.adv
+
+#DLLHeader
+ShString.HEL
diff --git a/test/testSA.ALD b/test/testSA.ALD
index 22eb3b0..4092c57 100644
Binary files a/test/testSA.ALD and b/test/testSA.ALD differ
diff --git a/test/xsys35c.cfg b/test/xsys35c.cfg
index 6fed47b..9244823 100644
--- a/test/xsys35c.cfg
+++ b/test/xsys35c.cfg
@@ -1,3 +1,5 @@
 ald_basename = test
-sys_ver = 3.8
+sys_ver = 3.9
 hed = test.hed
+disable_ain_variable = 1
+disable_ain_message = 1