diff --git a/src/hotspot/os/linux/cgroupSubsystem_linux.cpp b/src/hotspot/os/linux/cgroupSubsystem_linux.cpp
index be9ff1440c0..560589c3602 100644
--- a/src/hotspot/os/linux/cgroupSubsystem_linux.cpp
+++ b/src/hotspot/os/linux/cgroupSubsystem_linux.cpp
@@ -661,7 +661,7 @@ bool CgroupController::read_numerical_key_value(const char* filename, const char
   for (; line != nullptr; line = fgets(buf, buf_len, fp)) {
     char after_key = line[key_len];
     if (strncmp(line, key, key_len) == 0
-          && isspace(after_key) != 0
+          && isspace((unsigned char) after_key) != 0
           && after_key != '\n') {
       // Skip key, skip space
       const char* value_substr = line + key_len + 1;
diff --git a/src/hotspot/os/linux/os_linux.cpp b/src/hotspot/os/linux/os_linux.cpp
index 00ee3519301..b56d4082354 100644
--- a/src/hotspot/os/linux/os_linux.cpp
+++ b/src/hotspot/os/linux/os_linux.cpp
@@ -1356,7 +1356,7 @@ void os::Linux::capture_initial_stack(size_t max_size) {
       i = 0;
       if (s) {
         // Skip blank chars
-        do { s++; } while (s && isspace(*s));
+        do { s++; } while (s && isspace((unsigned char) *s));
 
 #define _UFM UINTX_FORMAT
 #define _DFM INTX_FORMAT
@@ -5222,7 +5222,7 @@ static jlong slow_thread_cpu_time(Thread *thread, bool user_sys_cpu_time) {
   if (s == nullptr) return -1;
 
   // Skip blank chars
-  do { s++; } while (s && isspace(*s));
+  do { s++; } while (s && isspace((unsigned char) *s));
 
   count = sscanf(s,"%c %d %d %d %d %d %lu %lu %lu %lu %lu %lu %lu",
                  &cdummy, &idummy, &idummy, &idummy, &idummy, &idummy,
diff --git a/src/hotspot/share/runtime/arguments.cpp b/src/hotspot/share/runtime/arguments.cpp
index 10a4c06d53c..5f89384ba66 100644
--- a/src/hotspot/share/runtime/arguments.cpp
+++ b/src/hotspot/share/runtime/arguments.cpp
@@ -748,7 +748,7 @@ static bool set_bool_flag(JVMFlag* flag, bool value, JVMFlagOrigin origin) {
 
 static bool set_fp_numeric_flag(JVMFlag* flag, const char* value, JVMFlagOrigin origin) {
   // strtod allows leading whitespace, but our flag format does not.
-  if (*value == '\0' || isspace(*value)) {
+  if (*value == '\0' || isspace((unsigned char) *value)) {
     return false;
   }
   char* end;
@@ -1178,13 +1178,13 @@ bool Arguments::process_settings_file(const char* file_name, bool should_exist,
         if (c == '\n') in_comment = false;
       } else {
         if (c == '#') in_comment = true;
-        else if (!isspace(c)) {
+        else if (!isspace((unsigned char) c)) {
           in_white_space = false;
           token[pos++] = checked_cast<char>(c);
         }
       }
     } else {
-      if (c == '\n' || (!in_quote && isspace(c))) {
+      if (c == '\n' || (!in_quote && isspace((unsigned char) c))) {
         // token ends at newline, or at unquoted whitespace
         // this allows a way to include spaces in string-valued options
         token[pos] = '\0';
@@ -3141,7 +3141,7 @@ jint Arguments::parse_options_buffer(const char* name, char* buffer, const size_
   // parse all options
   while (rd < buffer_end) {
     // skip leading white space from the input string
-    while (rd < buffer_end && isspace(*rd)) {
+    while (rd < buffer_end && isspace((unsigned char) *rd)) {
       rd++;
     }
 
@@ -3154,7 +3154,7 @@ jint Arguments::parse_options_buffer(const char* name, char* buffer, const size_
 
     // Tokens are strings of non white space characters separated
     // by one or more white spaces.
-    while (rd < buffer_end && !isspace(*rd)) {
+    while (rd < buffer_end && !isspace((unsigned char) *rd)) {
       if (*rd == '\'' || *rd == '"') {      // handle a quoted string
         int quote = *rd;                    // matching quote to look for
         rd++;                               // don't copy open quote
diff --git a/src/hotspot/share/services/diagnosticFramework.cpp b/src/hotspot/share/services/diagnosticFramework.cpp
index 006c08cb63f..984122f2777 100644
--- a/src/hotspot/share/services/diagnosticFramework.cpp
+++ b/src/hotspot/share/services/diagnosticFramework.cpp
@@ -45,7 +45,7 @@ CmdLine::CmdLine(const char* line, size_t len, bool no_command_name)
   line_end = &line[len];
 
   // Skip whitespace in the beginning of the line.
-  while (_cmd < line_end && isspace((int) _cmd[0])) {
+  while (_cmd < line_end && isspace((unsigned char) _cmd[0])) {
     _cmd++;
   }
   cmd_end = _cmd;
@@ -55,7 +55,7 @@ CmdLine::CmdLine(const char* line, size_t len, bool no_command_name)
     _cmd_len = 0;
   } else {
     // Look for end of the command name
-    while (cmd_end < line_end && !isspace((int) cmd_end[0])) {
+    while (cmd_end < line_end && !isspace((unsigned char) cmd_end[0])) {
       cmd_end++;
     }
     _cmd_len = cmd_end - _cmd;
diff --git a/src/java.base/share/native/libjli/args.c b/src/java.base/share/native/libjli/args.c
index 379291fe8ec..1e9b48730a9 100644
--- a/src/java.base/share/native/libjli/args.c
+++ b/src/java.base/share/native/libjli/args.c
@@ -501,7 +501,7 @@ static jboolean expand(JLI_List args, const char *str, const char *var_name) {
     // This is retained until the process terminates as it is saved as the args
     p = JLI_MemAlloc(JLI_StrLen(str) + 1);
     while (*str != '\0') {
-        while (*str != '\0' && isspace(*str)) {
+        while (*str != '\0' && isspace((unsigned char) *str)) {
             str++;
         }
 
@@ -511,7 +511,7 @@ static jboolean expand(JLI_List args, const char *str, const char *var_name) {
         }
 
         arg = p;
-        while (*str != '\0' && !isspace(*str)) {
+        while (*str != '\0' && !isspace((unsigned char) *str)) {
             if (inEnvVar && (*str == '"' || *str == '\'')) {
                 quote = *str++;
                 while (*str != quote && *str != '\0') {
@@ -577,7 +577,7 @@ static jboolean expand(JLI_List args, const char *str, const char *var_name) {
             exit(1);
         }
 
-        assert (*str == '\0' || isspace(*str));
+        assert (*str == '\0' || isspace((unsigned char) *str));
     }
 
     return JNI_TRUE;
diff --git a/src/jdk.hotspot.agent/linux/native/libsaproc/ps_proc.c b/src/jdk.hotspot.agent/linux/native/libsaproc/ps_proc.c
index 3068f475626..41207b5a9df 100644
--- a/src/jdk.hotspot.agent/linux/native/libsaproc/ps_proc.c
+++ b/src/jdk.hotspot.agent/linux/native/libsaproc/ps_proc.c
@@ -242,7 +242,7 @@ static bool process_doesnt_exist(pid_t pid) {
       found_state = true;
       state = buf + state_len;
       // Skip the spaces
-      while (isspace(*state)) {
+      while (isspace((unsigned char) *state)) {
         state++;
       }
       // A state value of 'X' indicates that the thread is dead. 'Z'
diff --git a/src/jdk.jdwp.agent/unix/native/libjdwp/exec_md.c b/src/jdk.jdwp.agent/unix/native/libjdwp/exec_md.c
index a694bba93c4..a0f2687a88c 100644
--- a/src/jdk.jdwp.agent/unix/native/libjdwp/exec_md.c
+++ b/src/jdk.jdwp.agent/unix/native/libjdwp/exec_md.c
@@ -35,14 +35,14 @@
 #include "error_messages.h"
 
 static char *skipWhitespace(char *p) {
-    while ((*p != '\0') && isspace(*p)) {
+    while ((*p != '\0') && isspace((unsigned char) *p)) {
         p++;
     }
     return p;
 }
 
 static char *skipNonWhitespace(char *p) {
-    while ((*p != '\0') && !isspace(*p)) {
+    while ((*p != '\0') && !isspace((unsigned char) *p)) {
         p++;
     }
     return p;
diff --git a/src/jdk.jpackage/share/native/common/ErrorHandling.cpp b/src/jdk.jpackage/share/native/common/ErrorHandling.cpp
index b3f7206bfc1..a3a4c2a9dfe 100644
--- a/src/jdk.jpackage/share/native/common/ErrorHandling.cpp
+++ b/src/jdk.jpackage/share/native/common/ErrorHandling.cpp
@@ -72,7 +72,7 @@ std::string makeMessage(const std::runtime_error& e, const SourceCodePos& pos) {
 namespace {
 
 bool isNotSpace(int chr) {
-    return isspace(chr) == 0;
+    return isspace((unsigned char) chr) == 0;
 }