diff --git a/linux-user/user-mmap.h b/linux-user/user-mmap.h
index 7265c2c116..2c9d99ed6c 100644
--- a/linux-user/user-mmap.h
+++ b/linux-user/user-mmap.h
@@ -18,6 +18,39 @@
 #ifndef LINUX_USER_USER_MMAP_H
 #define LINUX_USER_USER_MMAP_H
 
+#if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
+#ifdef TARGET_AARCH64
+# define TASK_UNMAPPED_BASE  0x5500000000
+#else
+# define TASK_UNMAPPED_BASE  (1ul << 38)
+#endif
+#else
+#ifdef TARGET_HPPA
+# define TASK_UNMAPPED_BASE  0xfa000000
+#else
+# define TASK_UNMAPPED_BASE  0x40000000
+#endif
+#endif
+
+/*
+ * Guest parameters for the ADDR_COMPAT_LAYOUT personality
+ * (at present this is the only layout supported by QEMU).
+ *
+ * TASK_UNMAPPED_BASE: For mmap without hint (addr != 0), the search
+ * for unused virtual memory begins at TASK_UNMAPPED_BASE.
+ *
+ * task_unmapped_base: When the guest address space is limited via -R,
+ * the value of TASK_UNMAPPED_BASE is adjusted to fit.
+ */
+extern abi_ulong task_unmapped_base;
+
+/*
+ * mmap_next_start: The base address for the next mmap without hint,
+ * increased after each successful map, starting at task_unmapped_base.
+ * This is an optimization within QEMU and not part of ADDR_COMPAT_LAYOUT.
+ */
+extern abi_ulong mmap_next_start;
+
 int target_mprotect(abi_ulong start, abi_ulong len, int prot);
 abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
                      int flags, int fd, off_t offset);
@@ -26,7 +59,6 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
                        abi_ulong new_size, unsigned long flags,
                        abi_ulong new_addr);
 abi_long target_madvise(abi_ulong start, abi_ulong len_in, int advice);
-extern abi_ulong mmap_next_start;
 abi_ulong mmap_find_vma(abi_ulong, abi_ulong, abi_ulong);
 void mmap_fork_start(void);
 void mmap_fork_end(int child);
diff --git a/linux-user/main.c b/linux-user/main.c
index 556956c363..be621dc792 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -821,6 +821,34 @@ int main(int argc, char **argv, char **envp)
         reserved_va = max_reserved_va;
     }
 
+    /*
+     * Temporarily disable
+     *   "comparison is always false due to limited range of data type"
+     * due to comparison between (possible) uint64_t and uintptr_t.
+     */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wtype-limits"
+
+    /*
+     * Select an initial value for task_unmapped_base that is in range.
+     */
+    if (reserved_va) {
+        if (TASK_UNMAPPED_BASE < reserved_va) {
+            task_unmapped_base = TASK_UNMAPPED_BASE;
+        } else {
+            /* The most common default formula is TASK_SIZE / 3. */
+            task_unmapped_base = TARGET_PAGE_ALIGN(reserved_va / 3);
+        }
+    } else if (TASK_UNMAPPED_BASE < UINTPTR_MAX) {
+        task_unmapped_base = TASK_UNMAPPED_BASE;
+    } else {
+        /* 32-bit host: pick something medium size. */
+        task_unmapped_base = 0x10000000;
+    }
+    mmap_next_start = task_unmapped_base;
+
+#pragma GCC diagnostic pop
+
     {
         Error *err = NULL;
         if (seed_optarg != NULL) {
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index eb04fab8ab..84436d45c8 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -299,20 +299,8 @@ static bool mmap_frag(abi_ulong real_start, abi_ulong start, abi_ulong last,
     return true;
 }
 
-#if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
-#ifdef TARGET_AARCH64
-# define TASK_UNMAPPED_BASE  0x5500000000
-#else
-# define TASK_UNMAPPED_BASE  (1ul << 38)
-#endif
-#else
-#ifdef TARGET_HPPA
-# define TASK_UNMAPPED_BASE  0xfa000000
-#else
-# define TASK_UNMAPPED_BASE  0x40000000
-#endif
-#endif
-abi_ulong mmap_next_start = TASK_UNMAPPED_BASE;
+abi_ulong task_unmapped_base;
+abi_ulong mmap_next_start;
 
 /*
  * Subroutine of mmap_find_vma, used when we have pre-allocated
@@ -391,7 +379,7 @@ abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong align)
 
             if ((addr & (align - 1)) == 0) {
                 /* Success.  */
-                if (start == mmap_next_start && addr >= TASK_UNMAPPED_BASE) {
+                if (start == mmap_next_start && addr >= task_unmapped_base) {
                     mmap_next_start = addr + size;
                 }
                 return addr;
