diff --git a/.gitignore b/.gitignore
index 5093f2e..d656a77 100644
--- a/.gitignore
+++ b/.gitignore
@@ -42,6 +42,7 @@ config.status
 config.sub
 configure
 configure.scan
+configure.ac~
 depcomp
 install-sh
 libtool
@@ -86,6 +87,7 @@ test/junk_data
 test/s3proxy-*
 test/write_multiblock
 test/mknod_test
+test/truncate_read_file
 
 #
 # Windows ports
diff --git a/src/fdcache_page.cpp b/src/fdcache_page.cpp
index ffc79b9..4eeff19 100644
--- a/src/fdcache_page.cpp
+++ b/src/fdcache_page.cpp
@@ -456,7 +456,13 @@ bool PageList::Resize(off_t size, bool is_loaded, bool is_modified)
     off_t total = Size();
 
     if(0 == total){
+        // [NOTE]
+        // The is_shrink flag remains unchanged in this function.
+        //
+        bool backup_is_shrink = is_shrink;
+
         Init(size, is_loaded, is_modified);
+        is_shrink = backup_is_shrink;
 
     }else if(total < size){
         // add new area
diff --git a/src/metaheader.cpp b/src/metaheader.cpp
index fc6f630..571dd6e 100644
--- a/src/metaheader.cpp
+++ b/src/metaheader.cpp
@@ -245,7 +245,7 @@ gid_t get_gid(const headers_t& meta)
 
 blkcnt_t get_blocks(off_t size)
 {
-    return size / 512 + 1;
+    return (size / 512) + (0 == (size % 512) ? 0 : 1);
 }
 
 time_t cvtIAMExpireStringToTime(const char* s)
diff --git a/src/s3fs.cpp b/src/s3fs.cpp
index 3d3eeae..bc7cb4c 100644
--- a/src/s3fs.cpp
+++ b/src/s3fs.cpp
@@ -2682,19 +2682,32 @@ static int s3fs_open(const char* _path, struct fuse_file_info* fi)
         return result;
     }
 
+    AutoFdEntity autoent;
+    FdEntity*    ent;
+    headers_t    meta;
+
     if((unsigned int)fi->flags & O_TRUNC){
         if(0 != st.st_size){
             st.st_size = 0;
             needs_flush = true;
         }
+    }else{
+        // [NOTE]
+        // If the file has already been opened and edited, the file size in
+        // the edited state is given priority.
+        // This prevents the file size from being reset to its original size
+        // if you keep the file open, shrink its size, and then read the file
+        // from another process while it has not yet been flushed.
+        //
+        if(NULL != (ent = autoent.OpenExistFdEntity(path)) && ent->IsModified()){
+            // sets the file size being edited.
+            ent->GetSize(st.st_size);
+        }
     }
     if(!S_ISREG(st.st_mode) || S_ISLNK(st.st_mode)){
         st.st_mtime = -1;
     }
 
-    AutoFdEntity autoent;
-    FdEntity*    ent;
-    headers_t    meta;
     if(0 != (result = get_object_attribute(path, NULL, &meta, true, NULL, true))){    // no truncate cache
       return result;
     }
diff --git a/test/Makefile.am b/test/Makefile.am
index a57a18f..808c059 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -32,11 +32,13 @@ testdir = test
 noinst_PROGRAMS = \
     junk_data \
     write_multiblock \
-    mknod_test
+    mknod_test \
+    truncate_read_file
 
-junk_data_SOURCES = junk_data.c
-write_multiblock_SOURCES = write_multiblock.cc
-mknod_test_SOURCES = mknod_test.c
+junk_data_SOURCES          = junk_data.c
+write_multiblock_SOURCES   = write_multiblock.cc
+mknod_test_SOURCES         = mknod_test.c
+truncate_read_file_SOURCES = truncate_read_file.c
 
 #
 # Local variables:
diff --git a/test/integration-test-main.sh b/test/integration-test-main.sh
index 9f01fdc..ee6adc8 100755
--- a/test/integration-test-main.sh
+++ b/test/integration-test-main.sh
@@ -112,6 +112,28 @@ function test_truncate_shrink_file {
     rm_test_file "${BIG_TRUNCATE_TEST_FILE}"
 }
 
+function test_truncate_shrink_read_file {
+    describe "Testing truncate(shrink) and read file ..."
+
+    # Initiate file size is 1024, and shrink file size is 512
+    local init_size=1024
+    local shrink_size=512
+
+    # create file
+    dd if=/dev/urandom of="${TEST_TEXT_FILE}" bs="${init_size}" count=1
+
+    # truncate(shrink) file and read it before flusing
+    ../../truncate_read_file "${TEST_TEXT_FILE}" "${shrink_size}"
+
+    # check file size
+    check_file_size "${TEST_TEXT_FILE}" "${shrink_size}"
+
+    # Truncate the file to 1024 length
+    local t_size=1024
+
+    rm_test_file
+}
+
 function test_mv_file {
     describe "Testing mv file function ..."
     # if the rename file exists, delete it
@@ -2610,6 +2632,7 @@ function add_all_tests {
     add_tests test_truncate_upload
     add_tests test_truncate_empty_file
     add_tests test_truncate_shrink_file
+    add_tests test_truncate_shrink_read_file
     add_tests test_mv_file
     add_tests test_mv_to_exist_file
     add_tests test_mv_empty_directory
diff --git a/test/truncate_read_file.c b/test/truncate_read_file.c
new file mode 100644
index 0000000..2959439
--- /dev/null
+++ b/test/truncate_read_file.c
@@ -0,0 +1,81 @@
+/*
+ * s3fs - FUSE-based file system backed by Amazon S3
+ *
+ * Copyright(C) 2021 Andrew Gaul <andrew@gaul.org>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+// [NOTE]
+// This is a program used for file size inspection.
+// File size checking should be done by the caller of this program.
+// This program truncates the file and reads the file in another process
+// between truncate and flush(close file).
+//
+int main(int argc, char *argv[])
+{
+    if(argc != 3){
+        fprintf(stderr, "[ERROR] Wrong paraemters\n");
+        fprintf(stdout, "[Usage] truncate_read_file <file path> <truncate size(bytes)>\n");
+        exit(EXIT_FAILURE);
+    }
+
+    const char* filepath = argv[1];
+    off_t       size     = (off_t)strtoull(argv[2], NULL, 10);
+    int         fd;
+
+    // open file
+    if(-1 == (fd = open(filepath, O_RDWR))){
+        fprintf(stderr, "[ERROR] Could not open file(%s)\n", filepath);
+        exit(EXIT_FAILURE);
+    }
+
+    // truncate
+    if(0 != ftruncate(fd, size)){
+        fprintf(stderr, "[ERROR] Could not truncate file(%s) to %lld byte.\n", filepath, (long long)size);
+        close(fd);
+        exit(EXIT_FAILURE);
+    }
+
+    // run sub-process for reading file(cat)
+    char szCommand[1024];
+    sprintf(szCommand, "cat %s >/dev/null 2>&1", filepath);
+    if(0 != system(szCommand)){
+        fprintf(stderr, "[ERROR] Failed to run sub-process(cat).\n");
+        close(fd);
+        exit(EXIT_FAILURE);
+    }
+
+    // close file(flush)
+    close(fd);
+
+    exit(EXIT_SUCCESS);
+}
+
+/*
+* Local variables:
+* tab-width: 4
+* c-basic-offset: 4
+* End:
+* vim600: expandtab sw=4 ts=4 fdm=marker
+* vim<600: expandtab sw=4 ts=4
+*/