diff --git a/src/java.base/share/native/libjli/args.c b/src/java.base/share/native/libjli/args.c
index 0994eaead1b..1c4f7f8cda1 100644
--- a/src/java.base/share/native/libjli/args.c
+++ b/src/java.base/share/native/libjli/args.c
@@ -23,6 +23,12 @@
  * questions.
  */
 
+/*
+ * ===========================================================================
+ * (c) Copyright IBM Corp. 2023, 2023 All Rights Reserved
+ * ===========================================================================
+ */
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <assert.h>
@@ -78,6 +84,7 @@ static jboolean expectingNoDashArg = JNI_FALSE;
 static size_t argsCount = 1;
 static jboolean stopExpansion = JNI_FALSE;
 static jboolean relaunch = JNI_FALSE;
+static jboolean parsingOpenJ9Args = JNI_FALSE;
 
 /*
  * Prototypes for internal functions.
@@ -422,6 +429,10 @@ JLI_PreprocessArg(const char *arg, jboolean expandSourceOpt) {
         return expandArg(arg);
     }
 
+    if (parsingOpenJ9Args && (JLI_StrCCmp(arg, "-Xoptionsfile=") == 0)) {
+        return expandArgFile(arg + 14);
+    }
+
     if (arg[0] != '@') {
         checkArg(arg);
         return NULL;
@@ -484,6 +495,42 @@ JLI_AddArgsFromEnvVar(JLI_List args, const char *var_name) {
     return expand(args, env, var_name);
 }
 
+JNIEXPORT jboolean JNICALL
+JLI_ParseOpenJ9ArgsFromEnvVar(JLI_List args, const char *var_name) {
+    const char *env = getenv(var_name);
+    jboolean result = JNI_FALSE;
+
+    /* Save the state. */
+    int savedFirstAppArgIndex = firstAppArgIndex;
+    jboolean savedExpectingNoDashArg = expectingNoDashArg;
+    size_t savedArgsCount = argsCount;
+    jboolean savedStopExpansion = stopExpansion;
+    jboolean savedRelaunch = relaunch;
+
+     if (NULL == env) {
+        return JNI_FALSE;
+    }
+
+    parsingOpenJ9Args = JNI_TRUE;
+    firstAppArgIndex = NOT_FOUND;
+    expectingNoDashArg = JNI_FALSE;
+    argsCount = 1;
+    stopExpansion = JNI_FALSE;
+    relaunch = JNI_FALSE;
+
+    result = expand(args, env, var_name);
+
+    /* Restore the state. */
+    parsingOpenJ9Args = JNI_FALSE;
+    firstAppArgIndex = savedFirstAppArgIndex;
+    expectingNoDashArg = savedExpectingNoDashArg;
+    argsCount = savedArgsCount;
+    stopExpansion = savedStopExpansion;
+    relaunch = savedRelaunch;
+
+    return result;
+}
+
 /*
  * Expand a string into a list of args.
  * If the string is the result of looking up an environment variable,
@@ -497,9 +544,13 @@ static jboolean expand(JLI_List args, const char *str, const char *var_name) {
     char *p, *arg;
     char quote;
     JLI_List argsInFile;
+    char *argMem = NULL;
 
     // This is retained until the process terminates as it is saved as the args
     p = JLI_MemAlloc(JLI_StrLen(str) + 1);
+    if (parsingOpenJ9Args) {
+        argMem = p;
+    }
     while (*str != '\0') {
         while (*str != '\0' && isspace(*str)) {
             str++;
@@ -541,6 +592,10 @@ static jboolean expand(JLI_List args, const char *str, const char *var_name) {
                 }
                 exit(1);
             }
+            if (parsingOpenJ9Args) {
+                /* Dup the string so it can easily be freed later. */
+                arg = JLI_StringDup(arg);
+            }
             JLI_List_add(args, arg);
         } else {
             size_t cnt, idx;
@@ -580,6 +635,9 @@ static jboolean expand(JLI_List args, const char *str, const char *var_name) {
         assert (*str == '\0' || isspace(*str));
     }
 
+    if (parsingOpenJ9Args) {
+        JLI_MemFree(argMem);
+    }
     return JNI_TRUE;
 }
 
diff --git a/src/java.base/share/native/libjli/java.c b/src/java.base/share/native/libjli/java.c
index ba778e5e777..f99dae4e379 100644
--- a/src/java.base/share/native/libjli/java.c
+++ b/src/java.base/share/native/libjli/java.c
@@ -25,7 +25,7 @@
 
 /*
  * ===========================================================================
- * (c) Copyright IBM Corp. 2022, 2022 All Rights Reserved
+ * (c) Copyright IBM Corp. 2022, 2023 All Rights Reserved
  * ===========================================================================
  */
 
@@ -139,6 +139,8 @@ static jboolean ValidateModules(JNIEnv* env);
 
 static void SetPaths(int argc, char **argv);
 
+static int parse_size(const char *s, jlong *result);
+
 static void DumpState();
 
 enum OptionKind {
@@ -325,6 +327,31 @@ JLI_Launch(int argc, char ** argv,              /* main argc, argv */
         }
     }
 
+    {
+        /* Process -Xmso in the OPENJ9_JAVA_OPTIONS environment variable to
+         * set the main thread stack size. May be overridden by a later command
+         * line option.
+         */
+        JLI_List openj9Args = JLI_List_new(8); /* 8 is arbitrary */
+        if (JLI_ParseOpenJ9ArgsFromEnvVar(openj9Args, "OPENJ9_JAVA_OPTIONS")) {
+            size_t i = openj9Args->size;
+            while (i > 0) {
+                i -= 1;
+                if (JLI_StrCCmp(openj9Args->elements[i], "-Xmso") == 0) {
+                    jlong tmp = 0;
+                    if (parse_size(openj9Args->elements[i] + 5, &tmp)) {
+                        threadStackSize = tmp;
+                        if (threadStackSize > 0 && threadStackSize < (jlong)STACK_SIZE_MINIMUM) {
+                            threadStackSize = STACK_SIZE_MINIMUM;
+                        }
+                    }
+                    break;
+                }
+            }
+            JLI_List_free(openj9Args);
+        }
+    }
+
     /* Parse command line options; if the return value of
      * ParseArguments is false, the program should exit.
      */
diff --git a/src/java.base/share/native/libjli/jli_util.h b/src/java.base/share/native/libjli/jli_util.h
index 6aa26a04f77..d240d318aaa 100644
--- a/src/java.base/share/native/libjli/jli_util.h
+++ b/src/java.base/share/native/libjli/jli_util.h
@@ -23,6 +23,12 @@
  * questions.
  */
 
+/*
+ * ===========================================================================
+ * (c) Copyright IBM Corp. 2023, 2023 All Rights Reserved
+ * ===========================================================================
+ */
+
 #ifndef _JLI_UTIL_H
 #define _JLI_UTIL_H
 
@@ -158,4 +164,7 @@ JLI_PreprocessArg(const char *arg, jboolean expandSourceOpt);
 JNIEXPORT jboolean JNICALL
 JLI_AddArgsFromEnvVar(JLI_List args, const char *var_name);
 
+JNIEXPORT jboolean JNICALL
+JLI_ParseOpenJ9ArgsFromEnvVar(JLI_List args, const char *var_name);
+
 #endif  /* _JLI_UTIL_H */