diff --git a/lib/common/ipc_common.c b/lib/common/ipc_common.c
index 78fedbdd61..d0c06365cd 100644
--- a/lib/common/ipc_common.c
+++ b/lib/common/ipc_common.c
@@ -1,104 +1,110 @@
 /*
- * Copyright 2004-2020 the Pacemaker project contributors
+ * Copyright 2004-2021 the Pacemaker project contributors
  *
  * The version control history for this file may have further details.
  *
  * This source code is licensed under the GNU Lesser General Public License
  * version 2.1 or later (LGPLv2.1+) WITHOUT ANY WARRANTY.
  */
 
 #include <crm_internal.h>
 
 #include <stdio.h>
 #include <stdint.h>         // uint64_t
 #include <sys/types.h>
 
 #include <crm/msg_xml.h>
 #include "crmcommon_private.h"
 
 #define MIN_MSG_SIZE    12336    // sizeof(struct qb_ipc_connection_response)
 #define MAX_MSG_SIZE    128*1024 // 128k default
 
 /*!
  * \internal
  * \brief Choose an IPC buffer size in bytes
  *
  * \param[in] max  Use this value if environment/default is lower
  *
  * \return Maximum of max and value of PCMK_ipc_buffer (default 128KB)
  */
 unsigned int
 pcmk__ipc_buffer_size(unsigned int max)
 {
     static unsigned int global_max = 0;
 
     if (global_max == 0) {
-        const char *env = getenv("PCMK_ipc_buffer");
+        long long global_ll;
 
-        if (env) {
-            int env_max = crm_parse_int(env, "0");
+        if ((pcmk__scan_ll(getenv("PCMK_ipc_buffer"), &global_ll,
+                           0LL) != pcmk_rc_ok)
+            || (global_ll <= 0)) {
+            global_max = MAX_MSG_SIZE; // Default for unset or invalid
 
-            global_max = (env_max > 0)? QB_MAX(MIN_MSG_SIZE, env_max) : MAX_MSG_SIZE;
+        } else if (global_ll < MIN_MSG_SIZE) {
+            global_max = MIN_MSG_SIZE;
+
+        } else if (global_ll > UINT_MAX) {
+            global_max = UINT_MAX;
 
         } else {
-            global_max = MAX_MSG_SIZE;
+            global_max = (unsigned int) global_ll;
         }
     }
     return QB_MAX(max, global_max);
 }
 
 /*!
  * \brief Return pacemaker's default IPC buffer size
  *
  * \return IPC buffer size in bytes
  */
 unsigned int
 crm_ipc_default_buffer_size(void)
 {
     static unsigned int default_size = 0;
 
     if (default_size == 0) {
         default_size = pcmk__ipc_buffer_size(0);
     }
     return default_size;
 }
 
 /*!
  * \internal
  * \brief Check whether an IPC header is valid
  *
  * \param[in] header  IPC header to check
  *
  * \return true if IPC header has a supported version, false otherwise
  */
 bool
 pcmk__valid_ipc_header(const pcmk__ipc_header_t *header)
 {
     if (header == NULL) {
         crm_err("IPC message without header");
         return false;
 
     } else if (header->version > PCMK__IPC_VERSION) {
         crm_err("Filtering incompatible v%d IPC message (only versions <= %d supported)",
                 header->version, PCMK__IPC_VERSION);
         return false;
     }
     return true;
 }
 
 const char *
 pcmk__client_type_str(uint64_t client_type)
 {
     switch (client_type) {
         case pcmk__client_ipc:
             return "IPC";
         case pcmk__client_tcp:
             return "TCP";
 #ifdef HAVE_GNUTLS_GNUTLS_H
         case pcmk__client_tls:
             return "TLS";
 #endif
         default:
             return "unknown";
     }
 }