diff --git a/src/mmu.rs b/src/mmu.rs
index 59fe1c0..ffa5434 100644
--- a/src/mmu.rs
+++ b/src/mmu.rs
@@ -12,6 +12,7 @@ use crate::{
 const ID: u16 = 5;
 
 const TLB_MAPPING_FLAG_VALID: u32 = 0x800;
+const MAPPING_FLAG_EXECUTABLE: u32 = 0x8;
 const MAPPING_FLAG_USER: u32 = 0x4;
 const MAPPING_FLAG_WRITABLE: u32 = 0x2;
 const MAPPING_FLAG_PRESENT: u32 = 0x1;
@@ -177,14 +178,17 @@ impl Card for MmuCard {
                 let present_flag = (flags & MAPPING_FLAG_PRESENT) > 0;
                 let wr_flag = (flags & MAPPING_FLAG_WRITABLE) > 0;
                 let user_flag = (flags & MAPPING_FLAG_USER) > 0;
+                let exec_flag = (flags & MAPPING_FLAG_EXECUTABLE) > 0;
                 let present_flag = if present_flag { "P" } else { "_" };
                 let wr_flag = if wr_flag { "W" } else { "_" };
                 let user_flag = if user_flag { "U" } else { "_" };
+                let exec_flag = if exec_flag { "X" } else { "_" };
                 if j == i {
                     println!(
-                        "0x{:0>6x}: 0x{:0>8x} ({}{}{})",
+                        "0x{:0>6x}: 0x{:0>8x} ({}{}{}{})",
                         i << 12,
                         frame,
+                        exec_flag,
                         user_flag,
                         wr_flag,
                         present_flag
@@ -193,10 +197,11 @@ impl Card for MmuCard {
                 } else {
                     if range_one_page.unwrap() {
                         println!(
-                            "0x{:0>6x}-0x{:0>6x}: 0x{:0>8x} ({}{}{})",
+                            "0x{:0>6x}-0x{:0>6x}: 0x{:0>8x} ({}{}{}{})",
                             i << 12,
                             j << 12,
                             frame,
+                            exec_flag,
                             user_flag,
                             wr_flag,
                             present_flag
@@ -204,11 +209,12 @@ impl Card for MmuCard {
                     } else {
                         let range_len = (j - i) as u32;
                         println!(
-                            "0x{:0>6x}-0x{:0>6x}: 0x{:0>8x}-0x{:0>8x} ({}{}{})",
+                            "0x{:0>6x}-0x{:0>6x}: 0x{:0>8x}-0x{:0>8x} ({}{}{}{})",
                             i << 12,
                             j << 12,
                             frame,
                             frame + (range_len * 0x1000),
+                            exec_flag,
                             user_flag,
                             wr_flag,
                             present_flag
@@ -259,14 +265,17 @@ impl Card for MmuCard {
                 let present_flag = (flags & MAPPING_FLAG_PRESENT) > 0;
                 let wr_flag = (flags & MAPPING_FLAG_WRITABLE) > 0;
                 let user_flag = (flags & MAPPING_FLAG_USER) > 0;
+                let exec_flag = (flags & MAPPING_FLAG_EXECUTABLE) > 0;
                 let present_flag = if present_flag { "P" } else { "_" };
                 let wr_flag = if wr_flag { "W" } else { "_" };
                 let user_flag = if user_flag { "U" } else { "_" };
+                let exec_flag = if exec_flag { "X" } else { "_" };
                 if j == i {
                     println!(
-                        "0x{:0>6x}: 0x{:0>8x} ({}{}{})",
+                        "0x{:0>6x}: 0x{:0>8x} ({}{}{}{})",
                         i << 12,
                         frame,
+                        exec_flag,
                         user_flag,
                         wr_flag,
                         present_flag
@@ -275,10 +284,11 @@ impl Card for MmuCard {
                 } else {
                     if range_one_page.unwrap() {
                         println!(
-                            "0x{:0>6x}-0x{:0>6x}: 0x{:0>8x} ({}{}{})",
+                            "0x{:0>6x}-0x{:0>6x}: 0x{:0>8x} ({}{}{}{})",
                             i << 12,
                             j << 12,
                             frame,
+                            exec_flag,
                             user_flag,
                             wr_flag,
                             present_flag
@@ -286,11 +296,12 @@ impl Card for MmuCard {
                     } else {
                         let range_len = (j - i) as u32;
                         println!(
-                            "0x{:0>6x}-0x{:0>6x}: 0x{:0>8x}-0x{:0>8x} ({}{}{})",
+                            "0x{:0>6x}-0x{:0>6x}: 0x{:0>8x}-0x{:0>8x} ({}{}{}{})",
                             i << 12,
                             j << 12,
                             frame,
                             frame + (range_len * 0x1000),
+                            exec_flag,
                             user_flag,
                             wr_flag,
                             present_flag
@@ -368,6 +379,12 @@ impl Mmu for MmuCard {
                 mapping
             };
             if mapping & MAPPING_FLAG_PRESENT > 0 {
+                if function.is_code() && (mapping & MAPPING_FLAG_EXECUTABLE == 0) {
+                    if print_debug {
+                        println!("Page not executable");
+                    }
+                    return NullableResult::Err(BusError);
+                }
                 if !function.is_supervisor() && (mapping & MAPPING_FLAG_USER == 0) {
                     if print_debug {
                         println!("Page not user accessible");