diff --git a/AvailableColumnsPanel.c b/AvailableColumnsPanel.c
index 70d75807..6865b8bc 100644
--- a/AvailableColumnsPanel.c
+++ b/AvailableColumnsPanel.c
@@ -54,7 +54,7 @@ static HandlerResult AvailableColumnsPanel_eventHandler(Panel* super, int ch) {
       }
       default:
       {
-         if (isalpha(ch))
+         if (ch < 255 && isalpha(ch))
             result = Panel_selectByTyping(super, ch);
          break;
       }
diff --git a/CategoriesPanel.c b/CategoriesPanel.c
index fe55a88a..8cb442e4 100644
--- a/CategoriesPanel.c
+++ b/CategoriesPanel.c
@@ -97,7 +97,7 @@ static HandlerResult CategoriesPanel_eventHandler(Panel* super, int ch) {
          break;
       }
       default:
-         if (isalpha(ch))
+         if (ch < 255 && isalpha(ch))
             result = Panel_selectByTyping(super, ch);
          if (result == BREAK_LOOP)
             result = IGNORED;
diff --git a/ColumnsPanel.c b/ColumnsPanel.c
index b2fa5b5e..918ee320 100644
--- a/ColumnsPanel.c
+++ b/ColumnsPanel.c
@@ -100,7 +100,7 @@ static HandlerResult ColumnsPanel_eventHandler(Panel* super, int ch) {
       }
       default:
       {
-         if (isalpha(ch))
+         if (ch < 255 && isalpha(ch))
             result = Panel_selectByTyping(super, ch);
          if (result == BREAK_LOOP)
             result = IGNORED;
diff --git a/IncSet.c b/IncSet.c
index fe8db49e..2eb77ef4 100644
--- a/IncSet.c
+++ b/IncSet.c
@@ -151,7 +151,7 @@ bool IncSet_handleKey(IncSet* this, int ch, Panel* panel, IncMode_GetPanelValue
          }
       }
       doSearch = false;
-   } else if (isprint((char)ch) && (mode->index < INCMODE_MAX)) {
+   } else if (ch < 255 && isprint((char)ch) && (mode->index < INCMODE_MAX)) {
       mode->buffer[mode->index] = ch;
       mode->index++;
       mode->buffer[mode->index] = 0;
diff --git a/Panel.c b/Panel.c
index 42cbbfce..42c5ef2f 100644
--- a/Panel.c
+++ b/Panel.c
@@ -431,7 +431,7 @@ HandlerResult Panel_selectByTyping(Panel* this, int ch) {
       this->eventHandlerState = calloc(100, 1);
    char* buffer = this->eventHandlerState;
 
-   if (isalnum(ch)) {
+   if (ch < 255 && isalnum(ch)) {
       int len = strlen(buffer);
       if (len < 99) {
          buffer[len] = ch;
diff --git a/RichString.c b/RichString.c
index 51914b08..22ffecb5 100644
--- a/RichString.c
+++ b/RichString.c
@@ -128,7 +128,7 @@ static inline void RichString_writeFrom(RichString* this, int attrs, const char*
    int newLen = from + len;
    RichString_setLen(this, newLen);
    for (int i = from, j = 0; i < newLen; i++, j++)
-      this->chptr[i] = (isprint(data_c[j]) ? data_c[j] : '?') | attrs;
+      this->chptr[i] = (data_c[j] >= 32 ? data_c[j] : '?') | attrs;
    this->chptr[newLen] = 0;
 }
 
diff --git a/htop.c b/htop.c
index 6b1584e2..211489bb 100644
--- a/htop.c
+++ b/htop.c
@@ -381,7 +381,7 @@ int main(int argc, char** argv) {
          continue;
       }
       
-      if (isdigit((char)ch)) {
+      if (ch < 255 && isdigit((char)ch)) {
          if (Panel_size(panel) == 0) continue;
          pid_t pid = ch-48 + acc;
          for (int i = 0; i < ProcessList_size(pl); i++) {