diff --git a/src/dart.c b/src/dart.c
index 1ed9b214..2a5f2e69 100644
--- a/src/dart.c
+++ b/src/dart.c
@@ -559,10 +559,10 @@ u64 dart_search(dart_dev_t *dart, void *paddr)
         }
     }
 
-    return 0;
+    return DART_PTR_ERR;
 }
 
-s64 dart_find_iova(dart_dev_t *dart, s64 start, size_t len)
+u64 dart_find_iova(dart_dev_t *dart, s64 start, size_t len)
 {
     if (len % SZ_16K)
         return -1;
@@ -588,7 +588,7 @@ s64 dart_find_iova(dart_dev_t *dart, s64 start, size_t len)
             iova += SZ_16K;
     }
 
-    return -1;
+    return DART_PTR_ERR;
 }
 
 void dart_shutdown(dart_dev_t *dart)
diff --git a/src/dart.h b/src/dart.h
index c1c26698..254506bc 100644
--- a/src/dart.h
+++ b/src/dart.h
@@ -5,6 +5,9 @@
 
 #include "types.h"
 
+#define DART_PTR_ERR     BIT(63)
+#define DART_IS_ERR(val) FIELD_GET(DART_PTR_ERR, val)
+
 typedef struct dart_dev dart_dev_t;
 
 enum dart_type_t {
@@ -21,7 +24,7 @@ void dart_unmap(dart_dev_t *dart, uintptr_t iova, size_t len);
 void dart_free_l2(dart_dev_t *dart, uintptr_t iova);
 void *dart_translate(dart_dev_t *dart, uintptr_t iova);
 u64 dart_search(dart_dev_t *dart, void *paddr);
-s64 dart_find_iova(dart_dev_t *dart, s64 start, size_t len);
+u64 dart_find_iova(dart_dev_t *dart, s64 start, size_t len);
 void dart_shutdown(dart_dev_t *dart);
 
 #endif
diff --git a/src/display.c b/src/display.c
index a9d90ae3..1aebbf0e 100644
--- a/src/display.c
+++ b/src/display.c
@@ -115,20 +115,20 @@ int display_get_vram(u64 *paddr, u64 *size)
 static uintptr_t display_map_fb(uintptr_t iova, u64 paddr, u64 size)
 {
     if (iova == 0) {
-        s64 iova_disp0 = 0;
-        s64 iova_dcp = 0;
+        u64 iova_disp0 = 0;
+        u64 iova_dcp = 0;
 
         iova_dcp = dart_find_iova(dcp->dart_dcp, iova_dcp, size);
-        if (iova_dcp < 0) {
+        if (DART_IS_ERR(iova_dcp)) {
             printf("display: failed to find IOVA for fb of %06zx bytes (dcp)\n", size);
-            return 0;
+            return iova_dcp;
         }
 
         // try to map the fb to the same IOVA on disp0
         iova_disp0 = dart_find_iova(dcp->dart_dcp, iova_dcp, size);
-        if (iova_disp0 < 0) {
+        if (DART_IS_ERR(iova_disp0)) {
             printf("display: failed to find IOVA for fb of %06zx bytes (disp0)\n", size);
-            return 0;
+            return iova_disp0;
         }
 
         // assume this results in the same IOVA, not sure if this is required but matches what iboot
@@ -136,7 +136,7 @@ static uintptr_t display_map_fb(uintptr_t iova, u64 paddr, u64 size)
         if (iova_disp0 != iova_dcp) {
             printf("display: IOVA mismatch for fb between dcp (%08lx) and disp0 (%08lx)\n",
                    (u64)iova_dcp, (u64)iova_disp0);
-            return 0;
+            return DART_PTR_ERR;
         }
 
         iova = iova_dcp;
@@ -145,14 +145,14 @@ static uintptr_t display_map_fb(uintptr_t iova, u64 paddr, u64 size)
     int ret = dart_map(dcp->dart_disp, iova, (void *)paddr, size);
     if (ret < 0) {
         printf("display: failed to map fb to dart-disp0\n");
-        return 0;
+        return DART_PTR_ERR;
     }
 
     ret = dart_map(dcp->dart_dcp, iova, (void *)paddr, size);
     if (ret < 0) {
         printf("display: failed to map fb to dart-dcp\n");
         dart_unmap(dcp->dart_disp, iova, size);
-        return 0;
+        return DART_PTR_ERR;
     }
 
     return iova;
@@ -182,10 +182,11 @@ int display_start_dcp(void)
     // Find the framebuffer DVA
     fb_dva = dart_search(dcp->dart_disp, (void *)cur_boot_args.video.base);
     // framebuffer is not mapped on the M1 Ultra Mac Studio
-    if (!fb_dva)
+    if (DART_IS_ERR(fb_dva))
         fb_dva = display_map_fb(0, pa, size);
-    if (!fb_dva) {
+    if (DART_IS_ERR(fb_dva)) {
         printf("display: failed to find display DVA\n");
+        fb_dva = 0;
         dcp_shutdown(dcp, false);
         return -1;
     }
@@ -377,8 +378,8 @@ int display_configure(const char *config)
 
         tmp_dva = iova_alloc(dcp->iovad_dcp, size);
 
-        ret = display_map_fb(tmp_dva, fb_pa, size);
-        if (ret < 0) {
+        tmp_dva = display_map_fb(tmp_dva, fb_pa, size);
+        if (DART_IS_ERR(tmp_dva)) {
             printf("display: failed to map new fb\n");
             return -1;
         }
@@ -395,9 +396,10 @@ int display_configure(const char *config)
         dart_unmap(dcp->dart_disp, fb_dva, fb_size);
         dart_unmap(dcp->dart_dcp, fb_dva, fb_size);
 
-        ret = display_map_fb(fb_dva, fb_pa, size);
-        if (ret < 0) {
+        fb_dva = display_map_fb(fb_dva, fb_pa, size);
+        if (DART_IS_ERR(fb_dva)) {
             printf("display: failed to map new fb\n");
+            fb_dva = 0;
             return -1;
         }