diff --git a/arch/x86/pagetables.c b/arch/x86/pagetables.c
index 289a907f..d8a120a7 100644
--- a/arch/x86/pagetables.c
+++ b/arch/x86/pagetables.c
@@ -128,6 +128,26 @@ static mfn_t get_cr3_mfn(cr3_t *cr3_entry) {
     return cr3_entry->mfn;
 }
 
+static inline void pgentry_fixup_flags(pgentry_t *entry, unsigned long flags) {
+    /* Our new flags may take precedence over previous ones if the new ones are more
+     * permissive. */
+    unsigned long entry_new = *entry;
+    entry_new |= flags & _PAGE_USER; /* USER may result in crash if we enabled SMAP */
+    entry_new |= flags & _PAGE_RW;
+    entry_new &= ~(flags & _PAGE_NX);
+    if (unlikely(*entry != entry_new)) {
+        char flags_str_old[16];
+        char flags_str_new[16];
+        printk("WARNING: Already-present PTE protection flags conflicts with our.\n"
+               "         Updating present flags: %s -> %s\n",
+               dump_pte_flags(flags_str_old, 16, (pte_t) *entry),
+               dump_pte_flags(flags_str_new, 16, (pte_t) entry_new));
+        *entry = entry_new;
+        barrier();
+        flush_tlb();
+    }
+}
+
 static mfn_t get_pgentry_mfn(mfn_t tab_mfn, pt_index_t index, unsigned long flags) {
     pgentry_t *tab, *entry;
     mfn_t mfn;
@@ -147,6 +167,10 @@ static mfn_t get_pgentry_mfn(mfn_t tab_mfn, pt_index_t index, unsigned long flag
         tab = init_map_mfn(mfn);
         memset(tab, 0, PAGE_SIZE);
     }
+    else {
+        /* Page table already exists but its flags may conflict with our. Maybe fixup */
+        pgentry_fixup_flags(entry, flags);
+    }
 
     return mfn;
 }
diff --git a/tests/unittests.c b/tests/unittests.c
index 20b13b99..8a6c379c 100644
--- a/tests/unittests.c
+++ b/tests/unittests.c
@@ -33,6 +33,7 @@
 #include <test.h>
 #include <usermode.h>
 
+#include <mm/pmm.h>
 #include <smp/smp.h>
 
 static char opt_string[4];
@@ -109,6 +110,12 @@ static unsigned long __user_text test_user_task_func3(void *arg) {
     return -16;
 }
 
+#define HIGH_USER_PTR _ptr(0xffffffff80222000)
+static unsigned long __user_text test_user_task_func4(void *arg) {
+    printf(USTR("access: %lx\n"), _ul(HIGH_USER_PTR));
+    return *(unsigned long *) HIGH_USER_PTR;
+}
+
 int unit_tests(void *_unused) {
     printk("\nLet the UNITTESTs begin\n");
     printk("Commandline parsing: %s\n", kernel_cmdline);
@@ -178,7 +185,7 @@ int unit_tests(void *_unused) {
     cpu_freq_expect("Prototyp Amazing Foo Two @ 1.00GHz", 1000000000);
 
     task_t *task1, *task2, *task_user1, *task_user1_se, *task_user1_int80, *task_user2,
-        *task_user3;
+        *task_user3, *task_user4;
 
     task1 = new_kernel_task("test1", test_kernel_task_func, _ptr(98));
     task2 = new_kernel_task("test2", test_kernel_task_func, _ptr(-99));
@@ -189,6 +196,14 @@ int unit_tests(void *_unused) {
         new_user_task("test1 user int80", test_user_task_func1_int80, NULL);
     task_user2 = new_user_task("test2 user", test_user_task_func2, NULL);
     task_user3 = new_user_task("test3 user", test_user_task_func3, NULL);
+    task_user4 = new_user_task("test4 user", test_user_task_func4, NULL);
+
+    vmap_4k(HIGH_USER_PTR + 0x1000, get_free_frame()->mfn, L1_PROT);
+    memset(HIGH_USER_PTR + 0x1000, 0, 0x1000);
+    vmap_user_4k(HIGH_USER_PTR, get_free_frame()->mfn, L1_PROT_USER);
+
+    /* Be sure that we can still touch this vmap despite the user vmap. */
+    BUG_ON(*(unsigned long *) (HIGH_USER_PTR + 0x1000) != 0);
 
     set_task_repeat(task1, 10);
     schedule_task(task1, get_bsp_cpu());
@@ -198,6 +213,7 @@ int unit_tests(void *_unused) {
     schedule_task(task_user1_int80, get_bsp_cpu());
     schedule_task(task_user2, get_cpu(1));
     schedule_task(task_user3, get_bsp_cpu());
+    schedule_task(task_user4, get_cpu(1));
 
     printk("Long mode to real mode transition:\n");
     long_to_real();