diff --git a/README b/README
index dfc5d78..f5b637f 100644
--- a/README
+++ b/README
@@ -305,6 +305,15 @@ ERROR HANDLING
     RPe_IRANGE (-28)
         Invalid [] range "%s-%s"
 
+    RPe_DUPLCH (-29)
+        Regexp modifier "%s" may not appear twice
+
+    RPe_EXCLCH (-30)
+        Regexp modifiers "%s" and "%s" are mutually exclusive
+
+    RPe_NEGCHR (-31)
+        Regexp modifier "%s" may not appear after the "-"
+
 EXTENSIONS
     Here are some ideas for extensions (sub-classes) for this module. Some
     of them may be absorbed into the core functionality of Regexp::Parser in
diff --git a/lib/Regexp/Parser.pm b/lib/Regexp/Parser.pm
index 9412df5..d007a99 100644
--- a/lib/Regexp/Parser.pm
+++ b/lib/Regexp/Parser.pm
@@ -706,6 +706,18 @@ False [] range "%s-%s"
 
 Invalid [] range "%s-%s"
 
+=item RPe_DUPLCH (-29)
+
+Regexp modifier "%s" may not appear twice
+
+=item RPe_EXCLCH (-30)
+
+Regexp modifiers "%s" and "%s" are mutually exclusive
+
+=item RPe_NEGCHR (-31)
+
+Regexp modifier "%s" may not appear after the "-"
+
 =back
 
 =head1 EXTENSIONS
diff --git a/lib/Regexp/Parser/Diagnostics.pm b/lib/Regexp/Parser/Diagnostics.pm
index 971cfd3..fce3fb4 100644
--- a/lib/Regexp/Parser/Diagnostics.pm
+++ b/lib/Regexp/Parser/Diagnostics.pm
@@ -34,5 +34,8 @@ use constant RPe_OUTPOS => --$ENUM, 'POSIX syntax [%s %s] belongs inside charact
 use constant RPe_EMPTYB => --$ENUM, 'Empty \%s{}';
 use constant RPe_FRANGE => --$ENUM, 'False [] range "%s-%s"';
 use constant RPe_IRANGE => --$ENUM, 'Invalid [] range "%s-%s"';
+use constant RPe_DUPLCH => --$ENUM, 'Regexp modifier "%s" may not appear twice';
+use constant RPe_EXCLCH => --$ENUM, 'Regexp modifiers "%s" and "%s" are mutually exclusive';
+use constant RPe_NEGCHR => --$ENUM, 'Regexp modifier "%s" may not appear after the "-"';
 
 1;
diff --git a/lib/Regexp/Parser/Handlers.pm b/lib/Regexp/Parser/Handlers.pm
index e700f73..4d959d2 100644
--- a/lib/Regexp/Parser/Handlers.pm
+++ b/lib/Regexp/Parser/Handlers.pm
@@ -734,10 +734,28 @@ sub init {
     &RxPOS -= length($on.$off);
     my $old = &RxPOS;
 
+    my $charset_seen = '';  # track first charset flag (a/d/l/u)
     for (split //, $on) {
       &RxPOS++;
       if (my $f = $S->can("FLAG_$_")) {
         my $v = $S->$f(1) and $r_on .= $_;
+        # charset flag conflict detection (Perl 5.14+)
+        if ($v && ($v & 0xF0)) {  # this is a charset flag
+          if ($charset_seen) {
+            if ($charset_seen eq $_ && $_ eq 'a') {
+              # aa (strict ASCII) is valid — continue
+            }
+            elsif ($charset_seen eq $_) {
+              # dd, ll, uu — doubled non-a charset flag
+              $S->error($S->RPe_DUPLCH, $_);
+            }
+            else {
+              # different charset flags — mutually exclusive
+              $S->error($S->RPe_EXCLCH, $charset_seen, $_);
+            }
+          }
+          $charset_seen = $_;
+        }
         # /xx: if x is already on, set the xx bit (Perl 5.26+)
         if ($_ eq 'x' && ($f_on & $v)) {
           $f_on |= 0x200;  # FLAG_xx
@@ -756,6 +774,10 @@ sub init {
         &RxPOS++;
         if (my $f = $S->can("FLAG_$_")) {
           my $v = $S->$f(0) and $r_off .= $_;
+          # charset flags may not appear after - (Perl 5.14+)
+          if ($v && ($v & 0xF0)) {
+            $S->error($S->RPe_NEGCHR, $_);
+          }
           # -xx: also turn off the xx bit (Perl 5.26+)
           if ($_ eq 'x' && ($f_off & $v)) {
             $f_off |= 0x200;  # FLAG_xx
diff --git a/t/11errors.t b/t/11errors.t
index a8f5233..143d9bb 100644
--- a/t/11errors.t
+++ b/t/11errors.t
@@ -263,6 +263,46 @@ warns_regex('(?o)',  'useless (?o) flag warning');
 # Negative flag forms too
 warns_regex('(?-g)', 'useless (?-g) flag warning');
 
+##
+## 9b. CHARSET FLAG CONFLICTS — RPe_DUPLCH, RPe_EXCLCH, RPe_NEGCHR
+##
+
+# Doubled non-a charset flags (Perl rejects these)
+fails_regex('(?dd:a)',   ($r->RPe_DUPLCH)[0],  'doubled d flag');
+fails_regex('(?ll:a)',   ($r->RPe_DUPLCH)[0],  'doubled l flag');
+fails_regex('(?uu:a)',   ($r->RPe_DUPLCH)[0],  'doubled u flag');
+
+# Mutually exclusive charset flags
+fails_regex('(?al:a)',   ($r->RPe_EXCLCH)[0],  'a and l mutually exclusive');
+fails_regex('(?ad:a)',   ($r->RPe_EXCLCH)[0],  'a and d mutually exclusive');
+fails_regex('(?au:a)',   ($r->RPe_EXCLCH)[0],  'a and u mutually exclusive');
+fails_regex('(?du:a)',   ($r->RPe_EXCLCH)[0],  'd and u mutually exclusive');
+fails_regex('(?dl:a)',   ($r->RPe_EXCLCH)[0],  'd and l mutually exclusive');
+fails_regex('(?lu:a)',   ($r->RPe_EXCLCH)[0],  'l and u mutually exclusive');
+
+# Charset flags not allowed after - (negation section)
+fails_regex('(?-a:a)',   ($r->RPe_NEGCHR)[0],  'charset a after -');
+fails_regex('(?-d:a)',   ($r->RPe_NEGCHR)[0],  'charset d after -');
+fails_regex('(?-l:a)',   ($r->RPe_NEGCHR)[0],  'charset l after -');
+fails_regex('(?-u:a)',   ($r->RPe_NEGCHR)[0],  'charset u after -');
+fails_regex('(?i-a:a)',  ($r->RPe_NEGCHR)[0],  'charset a after - with on-flags');
+fails_regex('(?i-al:a)', ($r->RPe_NEGCHR)[0],  'charset a after - mixed');
+
+# Valid charset flag usage
+parses_ok('(?aa:a)',     'aa (strict ASCII) is valid');
+parses_ok('(?a:a)',      'single a flag valid');
+parses_ok('(?d:a)',      'single d flag valid');
+parses_ok('(?l:a)',      'single l flag valid');
+parses_ok('(?u:a)',      'single u flag valid');
+parses_ok('(?ai:a)',     'charset a + modifier i valid');
+parses_ok('(?aai:a)',    'strict ASCII + modifier i valid');
+parses_ok('(?^a:a)',     'caret + charset a valid');
+parses_ok('(?^aa:a)',    'caret + strict ASCII valid');
+
+# Caret with charset conflicts should also fail
+fails_regex('(?^al:a)',  ($r->RPe_EXCLCH)[0],  'caret + a and l exclusive');
+fails_regex('(?^du:a)',  ($r->RPe_EXCLCH)[0],  'caret + d and u exclusive');
+
 ##
 ## 10. BAD ESCAPE IN CHARACTER CLASS WARNINGS — RPe_BADESC
 ##