diff --git a/lib/perl5db.pl b/lib/perl5db.pl
index c6678543c68e..914fe57858de 100644
--- a/lib/perl5db.pl
+++ b/lib/perl5db.pl
@@ -2033,19 +2033,12 @@ sub _DB__handle_c_command {
             # Qualify it to the current package unless it's
             # already qualified.
             $subname = $package . "::" . $subname
-            unless $subname =~ /::/;
+              unless $subname =~ /::/;
 
-            # find_sub will return "file:line_number" corresponding
-            # to where the subroutine is defined; we call find_sub,
-            # break up the return value, and assign it in one
-            # operation.
-            ( $file, $i ) = ( find_sub($subname) =~ /^(.*):(.*)$/ );
-
-            # Force the line number to be numeric.
-            $i = $i + 0;
+            my ($file, $s, $e) = do { subroutine_first_breakable_line($subname) };
 
             # If we got a line number, we found the sub.
-            if ($i) {
+            if ($s) {
 
                 # Switch all the debugger's internals around so
                 # we're actually working with that file.
@@ -2058,19 +2051,18 @@ sub _DB__handle_c_command {
                 # Scan forward to the first executable line
                 # after the 'sub whatever' line.
                 $max = $#dbline;
-                my $_line_num = $i;
-                while ($dbline[$_line_num] == 0 && $_line_num< $max)
+                my $_line_num = $s;
+                while ($dbline[$_line_num] == 0 && $_line_num <= $e)
                 {
                     $_line_num++;
                 }
                 $i = $_line_num;
             } ## end if ($i)
-
-            # We didn't find a sub by that name.
             else {
-                print $OUT "Subroutine $subname not found.\n";
-                next CMD;
+                  print $OUT $@;
+                  next CMD;
             }
+
         } ## end if ($subname =~ /\D/)
 
         # At this point, either the subname was all digits (an
@@ -5389,6 +5381,61 @@ sub subroutine_filename_lines {
     return (find_sub($subname) =~ /^(.*):(\d+)-(\d+)$/);
 } ## end sub subroutine_filename_lines
 
+=head2 subroutine_first_breakable(subname)
+
+Return the file and line number of the first breakable line in
+subname.
+
+Throws an error message if subname is not breakable, or cannot be
+found.
+
+=cut
+
+sub _first_breakable_via_B {
+    my ( $subname ) = @_;
+
+    my $cv = do {
+        no strict "refs";
+        *$subname{CODE};
+    };
+    ref $cv eq "CODE"
+      or return;
+
+    eval { require B; 1 }
+      or return;
+
+    my $bcv = B::svref_2object($cv);
+
+    # can't break on an XSUB
+    $bcv->XSUB
+      and die "Cannot break on XSUB $subname\n";
+
+    my $op = $bcv->START;
+    unless ($op->isa("B::NULL")) {
+        while (!$op->isa("B::NULL") && $op->name ne "dbstate") {
+            $op = $op->next;
+        }
+
+        unless ($op->isa("B::NULL")) {
+            return ( $op->file, $op->line, $op->line );
+        }
+    }
+    return;
+}
+
+sub subroutine_first_breakable_line {
+    my ( $subname ) = @_;
+
+    my ($file, $s, $e) = _first_breakable_via_B($subname);
+    unless ($file) {
+        # at the very least this allows miniperl to debug
+        ( $file, $s, $e ) = subroutine_filename_lines($subname)
+          or die "Subroutine $subname not found.\n";
+    }
+
+    return ($file, $s, $e );
+}
+
 =head3 break_subroutine(subname) (API)
 
 Places a break on the first line possible in the specified subroutine. Uses
@@ -5401,9 +5448,8 @@ sub break_subroutine {
     my $subname = shift;
 
     # Get filename, start, and end.
-    my ( $file, $s, $e ) = subroutine_filename_lines($subname)
-      or die "Subroutine $subname not found.\n";
-
+    my ( $file, $s, $e ) = eval { subroutine_first_breakable_line($subname) }
+      or die $@;
 
     # Null condition changes to '1' (always true).
     my $cond = @_ ? shift(@_) : 1;
@@ -8849,7 +8895,7 @@ =head2 C<find_sub>
 
 Tries to use C<%sub> first; if it can't find it there, it tries building a
 reference to the subroutine and uses C<CvGV_name_or_bust> to locate it,
-loading it into C<@sub> as a side effect (XXX I think). If it can't find it
+loading it into C<%sub> as a side effect (XXX I think). If it can't find it
 this way, it brute-force searches C<%sub>, checking for identical references.
 
 =cut
diff --git a/lib/perl5db.t b/lib/perl5db.t
index 8cbdcf155495..783c67459dc8 100644
--- a/lib/perl5db.t
+++ b/lib/perl5db.t
@@ -3491,6 +3491,65 @@ EOS
     $wrapper->output_like(qr/\bOK\b/, "check the line is IOK");
 }
 
+{
+    # https://github.com/Perl/perl5/issues/799
+    my $prog = <<'EOS';
+sub problem {
+    $SIG{__DIE__} = sub {
+        die "<b problem> will set a break point here.\n";
+    };    # The break point _should_ be set here.
+    warn "This line will run even if you enter <c problem>.\n";
+}
+&problem;
+EOS
+
+    my $wrapper = DebugWrap->new(
+        {
+            cmds =>
+            [
+                "b problem",
+                "c",
+                "q"
+            ],
+            prog => \$prog
+        }
+    );
+    $wrapper->contents_like(qr/The break point _should_/, "break at right place (b)");
+    $wrapper->output_unlike(qr/This line will run even if you enter <c problem>\./,
+                            "didn't run the wrong code (b)");
+
+    $wrapper = DebugWrap->new(
+        {
+            cmds =>
+            [
+                "c problem",
+                "q"
+            ],
+            prog => \$prog
+        }
+    );
+    $wrapper->contents_like(qr/The break point _should_/, "break at right place (c)");
+    $wrapper->output_unlike(qr/This line will run even if you enter <c problem>\./,
+                            "didn't run the wrong code (c)");
+}
+
+{
+    my $wrapper = DebugWrap->new(
+        {
+            cmds =>
+            [
+                "b B::svref_2object",
+                "q"
+            ],
+            prog => \<<'EOS'
+use B;
+print "Hello\n";
+EOS
+        }
+    );
+    $wrapper->contents_like(qr/Cannot break on XSUB B::svref_2object/, "can't break on XSUB");
+}
+
 done_testing();
 
 END {