diff --git a/src/prim/unix/prim.c b/src/prim/unix/prim.c
index da2e2902..f9f38f4e 100644
--- a/src/prim/unix/prim.c
+++ b/src/prim/unix/prim.c
@@ -142,8 +142,9 @@ void _mi_prim_mem_init( mi_os_mem_config_t* config )
     config->alloc_granularity = (size_t)psize;
     #if defined(_SC_PHYS_PAGES)
     long pphys = sysconf(_SC_PHYS_PAGES);
-    if (pphys > 0 && (size_t)pphys < (SIZE_MAX/(size_t)psize)) {
-      config->physical_memory_in_kib = (size_t)pphys * ((size_t)psize / MI_KiB);
+    const size_t psize_in_kib = (size_t)psize / MI_KiB;
+    if (psize_in_kib > 0 && pphys > 0 && (size_t)pphys <= (SIZE_MAX/psize_in_kib)) {
+      config->physical_memory_in_kib = (size_t)pphys * psize_in_kib;
     }
     #endif
   }
diff --git a/src/prim/windows/prim.c b/src/prim/windows/prim.c
index a248e934..12a7a5d9 100644
--- a/src/prim/windows/prim.c
+++ b/src/prim/windows/prim.c
@@ -154,7 +154,7 @@ void _mi_prim_mem_init( mi_os_mem_config_t* config )
     if (pGetPhysicallyInstalledSystemMemory != NULL) {
       ULONGLONG memInKiB = 0;
       if ((*pGetPhysicallyInstalledSystemMemory)(&memInKiB)) {
-        if (memInKiB > 0 && memInKiB < (SIZE_MAX / MI_KiB)) {
+        if (memInKiB > 0 && memInKiB <= SIZE_MAX) {
           config->physical_memory_in_kib = memInKiB;
         }
       }