diff --git a/src/modules/dbus/iface-core.c b/src/modules/dbus/iface-core.c
index 1b14195c5..88e9030e7 100644
--- a/src/modules/dbus/iface-core.c
+++ b/src/modules/dbus/iface-core.c
@@ -1442,7 +1442,7 @@ static bool contains_space(const char *string) {
     pa_assert(string);
 
     for (p = string; *p; ++p) {
-        if (isspace(*p))
+        if (isspace((unsigned char)*p))
             return true;
     }
 
diff --git a/src/pulse/proplist.c b/src/pulse/proplist.c
index 4e2901b3f..d8c640442 100644
--- a/src/pulse/proplist.c
+++ b/src/pulse/proplist.c
@@ -480,7 +480,7 @@ pa_proplist *pa_proplist_from_string(const char *s) {
                     goto success;
                 else if (*p == '=')
                     goto fail;
-                else if (!isspace(*p)) {
+                else if (!isspace((unsigned char)*p)) {
                     key = p;
                     state = KEY;
                     key_len = 1;
@@ -492,7 +492,7 @@ pa_proplist *pa_proplist_from_string(const char *s) {
                     goto fail;
                 else if (*p == '=')
                     state = VALUE_START;
-                else if (isspace(*p))
+                else if (isspace((unsigned char)*p))
                     state = AFTER_KEY;
                 else
                     key_len++;
@@ -503,7 +503,7 @@ pa_proplist *pa_proplist_from_string(const char *s) {
                     goto fail;
                 else if (*p == '=')
                     state = VALUE_START;
-                else if (!isspace(*p))
+                else if (!isspace((unsigned char)*p))
                     goto fail;
                 break;
 
@@ -523,7 +523,7 @@ pa_proplist *pa_proplist_from_string(const char *s) {
                     state = VALUE_DOUBLE_QUOTES;
                     value = p+1;
                     value_len = 0;
-                } else if (!isspace(*p)) {
+                } else if (!isspace((unsigned char)*p)) {
                     state = VALUE_SIMPLE;
                     value = p;
                     value_len = 1;
@@ -531,7 +531,7 @@ pa_proplist *pa_proplist_from_string(const char *s) {
                 break;
 
             case VALUE_SIMPLE:
-                if (*p == 0 || isspace(*p)) {
+                if (*p == 0 || isspace((unsigned char)*p)) {
                     if (proplist_setn(pl, key, key_len, value, value_len) < 0)
                         goto fail;
 
@@ -610,7 +610,7 @@ pa_proplist *pa_proplist_from_string(const char *s) {
                     (*p >= 'A' && *p <= 'F') ||
                     (*p >= 'a' && *p <= 'f')) {
                     value_len++;
-                } else if (*p == 0 || isspace(*p)) {
+                } else if (*p == 0 || isspace((unsigned char)*p)) {
 
                     if (proplist_sethex(pl, key, key_len, value, value_len) < 0)
                         goto fail;
diff --git a/src/pulsecore/core-util.c b/src/pulsecore/core-util.c
index 1eb534ab4..19c89a9d0 100644
--- a/src/pulsecore/core-util.c
+++ b/src/pulsecore/core-util.c
@@ -2332,7 +2332,7 @@ int pa_atou(const char *s, uint32_t *ret_u) {
     pa_assert(ret_u);
 
     /* strtoul() ignores leading spaces. We don't. */
-    if (isspace(*s)) {
+    if (isspace((unsigned char)*s)) {
         errno = EINVAL;
         return -1;
     }
@@ -2376,7 +2376,7 @@ int pa_atol(const char *s, long *ret_l) {
     pa_assert(ret_l);
 
     /* strtol() ignores leading spaces. We don't. */
-    if (isspace(*s)) {
+    if (isspace((unsigned char)*s)) {
         errno = EINVAL;
         return -1;
     }
@@ -2421,7 +2421,7 @@ int pa_atod(const char *s, double *ret_d) {
     pa_assert(ret_d);
 
     /* strtod() ignores leading spaces. We don't. */
-    if (isspace(*s)) {
+    if (isspace((unsigned char)*s)) {
         errno = EINVAL;
         return -1;
     }
diff --git a/src/pulsecore/ltdl-helper.c b/src/pulsecore/ltdl-helper.c
index 4e003c91a..cfdde26c3 100644
--- a/src/pulsecore/ltdl-helper.c
+++ b/src/pulsecore/ltdl-helper.c
@@ -53,7 +53,7 @@ pa_void_func_t pa_load_sym(lt_dlhandle handle, const char *module, const char *s
     sn = pa_sprintf_malloc("%s_LTX_%s", module, symbol);
 
     for (c = sn; *c; c++)
-        if (!isalnum(*c))
+        if (!isalnum((unsigned char)*c))
             *c = '_';
 
     f = (pa_void_func_t) lt_dlsym(handle, sn);
diff --git a/src/pulsecore/modargs.c b/src/pulsecore/modargs.c
index 7b683463e..b3c0313f3 100644
--- a/src/pulsecore/modargs.c
+++ b/src/pulsecore/modargs.c
@@ -131,7 +131,7 @@ pa_modargs *pa_modargs_new(const char *args, const char* const* valid_keys) {
             case WHITESPACE:
                 if (*p == '=')
                     goto fail;
-                else if (!isspace(*p)) {
+                else if (!isspace((unsigned char)*p)) {
                     key = p;
                     state = KEY;
                     key_len = 1;
@@ -141,7 +141,7 @@ pa_modargs *pa_modargs_new(const char *args, const char* const* valid_keys) {
             case KEY:
                 if (*p == '=')
                     state = VALUE_START;
-                else if (isspace(*p))
+                else if (isspace((unsigned char)*p))
                     goto fail;
                 else
                     key_len++;
@@ -156,7 +156,7 @@ pa_modargs *pa_modargs_new(const char *args, const char* const* valid_keys) {
                     state = VALUE_DOUBLE_QUOTES;
                     value = p+1;
                     value_len = 0;
-                } else if (isspace(*p)) {
+                } else if (isspace((unsigned char)*p)) {
                     if (add_key_value(ma,
                                       pa_xstrndup(key, key_len),
                                       pa_xstrdup(""),
@@ -175,7 +175,7 @@ pa_modargs *pa_modargs_new(const char *args, const char* const* valid_keys) {
                 break;
 
             case VALUE_SIMPLE:
-                if (isspace(*p)) {
+                if (isspace((unsigned char)*p)) {
                     if (add_key_value(ma,
                                       pa_xstrndup(key, key_len),
                                       pa_xstrndup(value, value_len),