diff --git a/CHANGELOG b/CHANGELOG
index ad2632a56..9394a870f 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -27,7 +27,20 @@
     install ECL on the preferred destination (specified with "--prefix"
     parameter given to configure script).
 
-* Pending changes since 26.3.27
+* Pending changes since 26.5.5
+
+* 26.5.5 changes since 26.3.27
+
+- bugfix: MAKE-PACKAGE destructively modified defining form's cons cells of
+  the package local nicknames, breaking package literals in bytecmp (#839)
+
+- bugfix: the first environment is now always page-aligned by using the
+  same allocation mechanism as all subsequent envs (#828)
+
+- bugfix: allow loading concatenated fasc files (#842)
+
+- bugfix: defclass does not redefine existing classes at compile time with
+  forward-referenced classes (#843)
 
 * 26.3.27 changes since 24.5.10
 
diff --git a/src/c/load.d b/src/c/load.d
index 3862c9857..cca9bb54f 100644
--- a/src/c/load.d
+++ b/src/c/load.d
@@ -157,21 +157,22 @@ si_load_bytecodes(cl_object source, cl_object verbose, cl_object print, cl_objec
       cl_index bds_ndx = ecl_progv(env, ECL_CONS_CAR(progv_list),
                                    ECL_CONS_CDR(progv_list));
       forms = read_forms(strm, ECL_T);
-      ecl_bds_unwind(env, bds_ndx);
-    }
-    while (!Null(forms)) {
-      if (ECL_LISTP(forms)) {
-        cl_object x = ECL_CONS_CAR(forms);
-        forms = ECL_CONS_CDR(forms);
-        if (ecl_t_of(x) == t_bytecodes) {
-          _ecl_funcall1(x);
-          if (Null(forms)) {
-            forms = read_forms(strm, ECL_NIL);
+
+      while (!Null(forms)) {
+        if (ECL_LISTP(forms)) {
+          cl_object x = ECL_CONS_CAR(forms);
+          forms = ECL_CONS_CDR(forms);
+          if (ecl_t_of(x) == t_bytecodes) {
+            _ecl_funcall1(x);
+            if (Null(forms)) {
+              forms = read_forms(strm, ECL_NIL);
+            }
+            continue;
           }
-          continue;
         }
+        FEerror("Corrupt bytecodes file ~S", 1, source);
       }
-      FEerror("Corrupt bytecodes file ~S", 1, source);
+      ecl_bds_unwind(env, bds_ndx);
     }
     {
       cl_object x;
diff --git a/src/c/main.d b/src/c/main.d
index 7f06fe6a7..f00464c1e 100644
--- a/src/c/main.d
+++ b/src/c/main.d
@@ -49,7 +49,6 @@
 /******************************* EXPORTS ******************************/
 
 const char *ecl_self;
-static struct cl_env_struct first_env;
 
 /************************ GLOBAL INITIALIZATION ***********************/
 
@@ -419,7 +418,7 @@ struct cl_core_struct cl_core = {
 
   .system_properties = ECL_NIL,
 
-  .first_env = &first_env,
+  .first_env = NULL,
 #ifdef ECL_THREADS
   .processes = ECL_NIL,
 #endif
@@ -498,6 +497,9 @@ cl_boot(int argc, char **argv)
   setbuf(stdin,  stdin_buf);
   setbuf(stdout, stdout_buf);
 #endif
+
+  /* The first environment must be available at all times. */
+  cl_core.first_env = _ecl_alloc_env(NULL);
   init_process();
 
   ARGC = argc;
diff --git a/src/c/package.d b/src/c/package.d
index e6d6e3238..1d89dba28 100644
--- a/src/c/package.d
+++ b/src/c/package.d
@@ -203,10 +203,10 @@ process_package_list(cl_object packages)
 }
 
 static cl_object
-process_local_nicknames_list(cl_object local_nicknames)
+process_local_nicknames_tree(cl_object local_nicknames)
 {
   cl_object l, nl;
-  local_nicknames = cl_copy_list(local_nicknames);
+  local_nicknames = cl_copy_tree(local_nicknames);
   for (l = local_nicknames; l != ECL_NIL; l = ECL_CONS_CDR(l)) {
     nl = ECL_CONS_CAR(l);
     ECL_RPLACA(nl, cl_string(ECL_CONS_CAR(nl)));
@@ -227,7 +227,7 @@ ecl_make_package(cl_object name, cl_object nicknames,
   name = cl_string(name);
   nicknames = process_nicknames(nicknames);
   use_list = process_package_list(use_list);
-  local_nicknames = process_local_nicknames_list(local_nicknames);
+  local_nicknames = process_local_nicknames_tree(local_nicknames);
 
   ECL_WITH_GLOBAL_ENV_WRLOCK_BEGIN(env) {
     if (ecl_option_values[ECL_OPT_BOOTED]) {
@@ -833,7 +833,8 @@ ecl_shadow(cl_object s, cl_object p)
       p->pack.internal = _ecl_sethash(s, p->pack.internal, x);
       x->symbol.hpack = p;
     }
-    p->pack.shadowings = CONS(x, p->pack.shadowings);
+    if (!ecl_member_eq(x, p->pack.shadowings))
+      p->pack.shadowings = CONS(x, p->pack.shadowings);
   } ECL_WITH_GLOBAL_ENV_WRLOCK_END;
 }
 
diff --git a/src/c/stacks.d b/src/c/stacks.d
index ef52372c6..08d49aeb4 100644
--- a/src/c/stacks.d
+++ b/src/c/stacks.d
@@ -281,7 +281,7 @@ ecl_stack_frame_open(cl_env_ptr env, cl_object f, cl_index size)
 
 /* Some clang versions miscompile the following function on x86_64.
  * Temporarily turn off optimizations here. */
-#if defined(__clang__) && __clang_major__ >= 17 && __clang_major__ <= 19 && defined(__x86_64__)
+#if defined(__clang__) && __clang_major__ >= 17 && __clang_major__ <= 22 && defined(__x86_64__)
 [[clang::optnone]]
 #endif
 void
@@ -341,7 +341,7 @@ ecl_stack_frame_push_values(cl_object f)
 
 /* Some clang versions miscompile the following function on x86_64.
  * Temporarily turn off optimizations here. */
-#if defined(__clang__) && __clang_major__ >= 17 && __clang_major__ <= 19 && defined(__x86_64__)
+#if defined(__clang__) && __clang_major__ >= 17 && __clang_major__ <= 22 && defined(__x86_64__)
 [[clang::optnone]]
 #endif
 cl_object
diff --git a/src/c/symbols_list.h b/src/c/symbols_list.h
index ff77ac41c..2a6992e8e 100644
--- a/src/c/symbols_list.h
+++ b/src/c/symbols_list.h
@@ -2043,6 +2043,7 @@ cl_symbols[] = {
 {EXT_ "ALLOW-WITH-INTERRUPTS" ECL_FUN(NULL, NULL, -1) ECL_VAR(MP_CONSTANT, OBJNULL)},
 
 {SYS_ "*QUIT-TAG*" ECL_FUN(NULL, NULL, -1) ECL_VAR(SI_SPECIAL, OBJNULL)},
+{SYS_ "*BREAK-LOCALS*" ECL_FUN(NULL, NULL, -1) ECL_VAR(SI_SPECIAL, ECL_NIL)},
 
 {EXT_ "ARRAY-RAW-DATA" ECL_FUN("si_array_raw_data", si_array_raw_data, 1) ECL_VAR(EXT_ORDINARY, OBJNULL)},
 
diff --git a/src/clos/boot.lsp b/src/clos/boot.lsp
index 51291f1d1..9d2d31426 100644
--- a/src/clos/boot.lsp
+++ b/src/clos/boot.lsp
@@ -18,13 +18,15 @@
 ;;; We cannot use the functions CREATE-STANDARD-CLASS and others because SLOTS,
 ;;; DIRECT-SLOTS, etc are empty and therefore SLOT-VALUE does not work.
 
-(defun make-empty-standard-class (name &key (metaclass 'standard-class)
-                                  direct-superclasses direct-slots index)
+(defun make-empty-standard-class
+    (name &key (metaclass 'standard-class)
+               direct-superclasses direct-slots index
+               (size #.(length +standard-class-slots+)))
   (declare (optimize speed (safety 0)))
-  (let* ((the-metaclass (and metaclass (gethash metaclass si::*class-name-hash-table*)))
+  (let* ((the-metaclass
+           (and metaclass (gethash metaclass si::*class-name-hash-table*)))
          (class (or (gethash name si::*class-name-hash-table*)
-                    (si:allocate-raw-instance nil the-metaclass
-                                              #.(length +standard-class-slots+)))))
+                    (si:allocate-raw-instance nil the-metaclass size))))
     (with-early-accessors (+standard-class-slots+)
       (when (eq name 'standard-class)
         (defconstant +the-standard-class+ class)
diff --git a/src/clos/hierarchy.lsp b/src/clos/hierarchy.lsp
index 33b5c4ca4..51538cef3 100644
--- a/src/clos/hierarchy.lsp
+++ b/src/clos/hierarchy.lsp
@@ -377,6 +377,7 @@
        :direct-slots #.+structure-class-slots+)
       (structure-object
        :metaclass structure-class
-       :direct-superclasses (t))
+       :direct-superclasses (t)
+       :size #.(length +structure-class-slots+))
       )))
 
diff --git a/src/cmp/cmpbackend-cxx/cmpc-inl-sysfun.lsp b/src/cmp/cmpbackend-cxx/cmpc-inl-sysfun.lsp
index 5f2c9074b..bf3c0fd03 100644
--- a/src/cmp/cmpbackend-cxx/cmpc-inl-sysfun.lsp
+++ b/src/cmp/cmpbackend-cxx/cmpc-inl-sysfun.lsp
@@ -636,7 +636,8 @@
     (def-inline cl:integerp :always (t) :bool "@0;ECL_FIXNUMP(#0)||ECL_BIGNUMP(#0)")
     (def-inline cl:floatp :always (t) :bool "floatp(#0)")
     (def-inline cl:characterp :always (t) :bool "ECL_CHARACTERP(#0)")
-    (def-inline si:base-char-p :always (character) :bool "ECL_BASE_CHAR_P(#0)")
+    (def-inline si:base-char-p :always (t) :bool "ECL_BASE_CHAR_P(#0)")
+    (def-inline si:base-char-p :always (character) :bool "ECL_BASE_CHAR_CODE_P(#0)")
     (def-inline cl:stringp :always (t) :bool "@0;ECL_STRINGP(#0)")
     (def-inline si:base-string-p :always (t) :bool "@0;ECL_BASE_STRING_P(#0)")
     (def-inline cl:bit-vector-p :always (t) :bool "@0;ECL_BIT_VECTOR_P(#0)")
diff --git a/src/cmp/cmpenv-proclaim.lsp b/src/cmp/cmpenv-proclaim.lsp
index 6394b4502..9bdd63b19 100644
--- a/src/cmp/cmpenv-proclaim.lsp
+++ b/src/cmp/cmpenv-proclaim.lsp
@@ -121,9 +121,12 @@
           (si:put-sysprop var 'CMP-TYPE type1))
         (warn "The variable name ~s is not a symbol." var))))
 
+;;; FIXME implement file-local global compiler environment for BCMP compiler and
+;;; unify compiler environment functions with CCMP.
 (defun si:proclaim-class (name class &optional (env c::*cmp-env-root*))
   "Add a class definition to the global compiler environment."
   (si:create-type-name name)
-  (ext:with-backend
-    :c/c++ (cmp-env-register-type name class c::*cmp-env-root*)
-    #-ecl-min :bytecodes #-ecl-min (setf (find-class name) class)))
+  (if *compiler-in-use*
+      (cmp-env-register-type name class c::*cmp-env-root*)
+      (or (find-class name nil)
+          (setf (find-class name) class))))
diff --git a/src/cmp/cmpmain.lsp b/src/cmp/cmpmain.lsp
index 1e8c86195..79a28fc93 100644
--- a/src/cmp/cmpmain.lsp
+++ b/src/cmp/cmpmain.lsp
@@ -206,7 +206,7 @@ after compilation."
         ((typep (setf def (fdefinition name)) 'standard-generic-function)
          (warn "COMPILE can not compile generic functions yet")
          (return-from compile (values def t nil)))
-        ((null (setq form (function-lambda-expression def)))
+        ((null (multiple-value-setq (form lexenv) (function-lambda-expression def)))
          (warn "We have lost the original function definition for ~s. Compilation to C failed"
                name)
          (return-from compile (values def t nil)))
diff --git a/src/configure b/src/configure
index dc0be976a..e197ef240 100755
--- a/src/configure
+++ b/src/configure
@@ -1,7 +1,7 @@
 #! /bin/sh
 # From configure.ac Revision.
 # Guess values for system-dependent variables and create Makefiles.
-# Generated by GNU Autoconf 2.72 for ecl 26.3.27.
+# Generated by GNU Autoconf 2.72 for ecl 26.5.5.
 #
 #
 # Copyright (C) 1992-1996, 1998-2017, 2020-2023 Free Software Foundation,
@@ -602,8 +602,8 @@ MAKEFLAGS=
 # Identity of this package.
 PACKAGE_NAME='ecl'
 PACKAGE_TARNAME='ecl'
-PACKAGE_VERSION='26.3.27'
-PACKAGE_STRING='ecl 26.3.27'
+PACKAGE_VERSION='26.5.5'
+PACKAGE_STRING='ecl 26.5.5'
 PACKAGE_BUGREPORT=''
 PACKAGE_URL=''
 
@@ -1404,7 +1404,7 @@ if test "$ac_init_help" = "long"; then
   # Omit some internal or obsolete options to make the list less imposing.
   # This message is too long to be a string in the A/UX 3.1 sh.
   cat <<_ACEOF
-'configure' configures ecl 26.3.27 to adapt to many kinds of systems.
+'configure' configures ecl 26.5.5 to adapt to many kinds of systems.
 
 Usage: $0 [OPTION]... [VAR=VALUE]...
 
@@ -1474,7 +1474,7 @@ fi
 
 if test -n "$ac_init_help"; then
   case $ac_init_help in
-     short | recursive ) echo "Configuration of ecl 26.3.27:";;
+     short | recursive ) echo "Configuration of ecl 26.5.5:";;
    esac
   cat <<\_ACEOF
 
@@ -1656,7 +1656,7 @@ fi
 test -n "$ac_init_help" && exit $ac_status
 if $ac_init_version; then
   cat <<\_ACEOF
-ecl configure 26.3.27
+ecl configure 26.5.5
 generated by GNU Autoconf 2.72
 
 Copyright (C) 2023 Free Software Foundation, Inc.
@@ -2258,7 +2258,7 @@ cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
 
-It was created by ecl $as_me 26.3.27, which was
+It was created by ecl $as_me 26.5.5, which was
 generated by GNU Autoconf 2.72.  Invocation command line was
 
   $ $0$ac_configure_args_raw
@@ -12386,7 +12386,7 @@ cat >>$CONFIG_STATUS <<\_ACEOF || ac_write_fail=1
 # report actual input values of CONFIG_FILES etc. instead of their
 # values after options handling.
 ac_log="
-This file was extended by ecl $as_me 26.3.27, which was
+This file was extended by ecl $as_me 26.5.5, which was
 generated by GNU Autoconf 2.72.  Invocation command line was
 
   CONFIG_FILES    = $CONFIG_FILES
@@ -12450,7 +12450,7 @@ ac_cs_config_escaped=`printf "%s\n" "$ac_cs_config" | sed "s/^ //; s/'/'\\\\\\\\
 cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 ac_cs_config='$ac_cs_config_escaped'
 ac_cs_version="\\
-ecl config.status 26.3.27
+ecl config.status 26.5.5
 configured by $0, generated by GNU Autoconf 2.72,
   with options \\"\$ac_cs_config\\"
 
diff --git a/src/configure.ac b/src/configure.ac
index 5eff9a037..af6f149c7 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -8,7 +8,7 @@ dnl  AUTOCONF configuration for ECL
 dnl  Giuseppe Attardi 25.1.1994
 dnl
 
-AC_INIT([ecl],[26.3.27],[])
+AC_INIT([ecl],[26.5.5],[])
 AC_REVISION([$Revision$])
 AC_CONFIG_SRCDIR([bare.lsp.in])
 AC_CONFIG_AUX_DIR([gmp])
diff --git a/src/lsp/predlib.lsp b/src/lsp/predlib.lsp
index ac2b2c550..36226eb17 100644
--- a/src/lsp/predlib.lsp
+++ b/src/lsp/predlib.lsp
@@ -36,13 +36,16 @@ Builds a new function which accepts any number of arguments but always outputs N
   (ext:fill-array-with-elt *subtypep-cache* nil 0 nil)
   (ext:fill-array-with-elt *upgraded-array-element-type-cache* nil 0 nil))
 
+;;; FIXME implement file-local global compiler environment for BCMP compiler and
+;;; unify compiler environment functions with CCMP.
 (defun proclaim-class (name class &optional env)
   "Add a class definition to the global compiler environment."
   (declare (ignore env))
-  ;; Default implementation for the bytecodes compiler which doesn't
-  ;; have a separate file-local compiler environment.
+  ;; Default implementation for the bytecodes compiler which doesn't have a
+  ;; separate file-local compiler environment.
   (si:create-type-name name)
-  (setf (find-class name) class))
+  (or (find-class name nil)
+      (setf (find-class name) class)))
 
 (defun create-type-name (name)
   (when (member name *alien-declarations*)
diff --git a/src/tests/ecl-tests.asd b/src/tests/ecl-tests.asd
index ec7b9963b..6872dca17 100644
--- a/src/tests/ecl-tests.asd
+++ b/src/tests/ecl-tests.asd
@@ -24,8 +24,8 @@
                          (:file "foreign-interface" :if-feature :ffi)
                          (:file "metaobject-protocol" :if-feature :clos)
                          (:file "ieee-fp" :if-feature :ieee-floating-point)
-                         (:file "package-extensions")
-			                (:file "hash-tables")
+                         (:file "packages")
+			 (:file "hash-tables")
                          (:file "external-formats" :if-feature :unicode)
                          (:file "unicode" :if-feature :unicode)
                          (:file "complex")
diff --git a/src/tests/ecl-tests.lisp b/src/tests/ecl-tests.lisp
index 1f471aa9b..cb950bd01 100644
--- a/src/tests/ecl-tests.lisp
+++ b/src/tests/ecl-tests.lisp
@@ -21,7 +21,7 @@
 
 ;;;; Declare the suites
 (suite 'make-check
-       '(executable ieee-fp eprocess package-ext hash-tables ansi+ mixed
+       '(executable ieee-fp eprocess packages hash-tables ansi+ mixed
          cmp emb ffi mop run-program mp complex wscl #+unicode unicode
          #+clos clos))
 
diff --git a/src/tests/normal-tests/compiler.lsp b/src/tests/normal-tests/compiler.lsp
index d425602c6..98d276573 100644
--- a/src/tests/normal-tests/compiler.lsp
+++ b/src/tests/normal-tests/compiler.lsp
@@ -2712,3 +2712,15 @@
           (with-compiler ("empty-file-0115.lsp" :load t))))
     (delete-file "empty-file-0115.lsp")
     (delete-file ofile)))
+
+;;; Date 2026-04-16
+;;; Description
+;;;
+;;;     Bytecodes compiler has problems with storing local packages nicknames.
+;;;     Error: "Cannot print object #<EXT package> readably."
+;;;
+(deftest cmp.0116.local-nicknames ()
+  (with-compiler ("local-nicknames-0116.lsp")
+    `(defpackage "ZET"
+       (:use)
+       (:local-nicknames ("E" "EXT")))))
diff --git a/src/tests/normal-tests/package-extensions.lsp b/src/tests/normal-tests/packages.lsp
similarity index 91%
rename from src/tests/normal-tests/package-extensions.lsp
rename to src/tests/normal-tests/packages.lsp
index 8ea249536..4444c4d33 100644
--- a/src/tests/normal-tests/package-extensions.lsp
+++ b/src/tests/normal-tests/packages.lsp
@@ -3,12 +3,13 @@
 
 ;;;; Author: Daniel Kochmański
 ;;;; Created: 2016-11-09
-;;;; Contains: PACKAGE extension tests
-;;;; Easter: Trump won the election today, we're doomed...
+;;;; Contains: PACKAGE tests
+;;;; Easter: Trump won the election today, we're screwed...
+;;;;         ([2026-03-30] told you so :-)
 
 (in-package :cl-test)
 
-(suite 'package-ext)
+(suite 'packages)
 
 (defmacro with-fresh-package (name &body body)
   `(progn
@@ -198,3 +199,20 @@
   (ignore-errors (delete-package :eu.turtleware.pack2))
   (ignore-errors (delete-package :eu.turtle.pack1))
   (ignore-errors (delete-package :eu.turtle.pack2)))
+
+;;; Reported by: Gábor Melis 
+;;; Created: 2026-03-30
+;;; Description
+;;;
+;;;     :shadow option may lead to duplicates in package-shadowing-symbols
+(deftest packages.0001.shadow-duplicates ()
+  (dotimes (x 3)
+    (defpackage "PACKAGES.0001.TTT"
+      (:shadow "CONS")
+      (:shadowing-import-from "EXT" "GC")
+      (:use "CL")))
+  (let ((shadowed-symbols (package-shadowing-symbols "PACKAGES.0001.TTT"))
+        (expected-symbols (list 'ext::gc
+                                (find-symbol "CONS" "PACKAGES.0001.TTT"))))
+    (is (= 2 (length shadowed-symbols)))
+    (is (null (set-difference shadowed-symbols expected-symbols)))))