diff --git a/src/defs.h b/src/defs.h
index 52db8d8..859ddce 100644
--- a/src/defs.h
+++ b/src/defs.h
@@ -25,7 +25,7 @@
 #include <stdint.h>
 #include <stddef.h>
 
-#define U6A_TOKEN_FN_CHAR ( 1 << 6 )
+#define U6A_TOKEN_FN_CHAR ( 1 << 4 )
 #define U6A_TOKEN_FN_APP  ( 1 << 5 )
 
 enum u6a_token_fn {
diff --git a/src/logging.c b/src/logging.c
index 3f7b4d1..c249987 100644
--- a/src/logging.c
+++ b/src/logging.c
@@ -98,8 +98,8 @@ u6a_err_cannot_open_file(const char* stage, const char* filename) {
 }
 
 U6A_COLD void
-u6a_err_stack_underflow(const char* stage, const char* description) {
-    fprintf(stderr, "%s: [%s] stack underflow error, %s.\n", prog_name, stage, description);
+u6a_err_stack_underflow(const char* stage) {
+    fprintf(stderr, "%s: [%s] stack underflow.\n", prog_name, stage);
 }
 
 U6A_COLD void
@@ -118,12 +118,17 @@ u6a_err_invalid_bc_file(const char* stage, const char* filename) {
     fprintf(stderr, "%s: [%s] %s is not a valid Unlambda bytecode file.\n", prog_name, stage, filename);
 }
 
-void
+U6A_COLD void
 u6a_err_bad_bc_ver(const char* stage, const char* filename, int ver_major, int ver_minor) {
     fprintf(stderr, "%s: [%s] bytecode file %s version %d.%d is not compatible.\n",
         prog_name, stage, filename, ver_major, ver_minor);
 }
 
+U6A_COLD void
+u6a_err_vm_pool_oom(const char* stage) {
+    fprintf(stderr, "%s: [%s] VM object pool memory exhausted.\n", stage, prog_name);
+}
+
 U6A_COLD void
 u6a_info_verbose_(const char* format, ...) {
     if (verbose) {
diff --git a/src/logging.h b/src/logging.h
index 1c161d4..35e26c6 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -63,7 +63,7 @@ void
 u6a_err_cannot_open_file(const char* stage, const char* filename);
 
 void
-u6a_err_stack_underflow(const char* stage, const char* description);
+u6a_err_stack_underflow(const char* stage);
 
 void
 u6a_err_invalid_uint(const char* stage, const char* str);
@@ -77,6 +77,9 @@ u6a_err_invalid_bc_file(const char* stage, const char* filename);
 void
 u6a_err_bad_bc_ver(const char* stage, const char* filename, int ver_major, int ver_minor);
 
+void
+u6a_err_vm_pool_oom(const char* stage);
+
 void
 u6a_info_verbose_(const char* format, ...);
 
diff --git a/src/runtime.c b/src/runtime.c
index 0d1f45d..c585de1 100644
--- a/src/runtime.c
+++ b/src/runtime.c
@@ -173,10 +173,10 @@ u6a_runtime_init(struct u6a_runtime_options* options) {
     if (UNLIKELY(rodata_len != fread(rodata, sizeof(char), rodata_len, options->istream))) {
         goto runtime_init_failed;
     }
-    if (UNLIKELY(!u6a_vm_stack_init(options->stack_segment_size))) {
+    if (UNLIKELY(!u6a_vm_stack_init(options->stack_segment_size, err_runtime))) {
         goto runtime_init_failed;
     }
-    if (UNLIKELY(!u6a_vm_pool_init(options->pool_size, text_len))) {
+    if (UNLIKELY(!u6a_vm_pool_init(options->pool_size, text_len, err_runtime))) {
         goto runtime_init_failed;
     }
     for (struct u6a_vm_ins* ins = text + text_subst_len; ins < text + text_len; ++ins) {
diff --git a/src/vm_pool.c b/src/vm_pool.c
index 42e3c2e..5c6bcce 100644
--- a/src/vm_pool.c
+++ b/src/vm_pool.c
@@ -19,6 +19,7 @@
 
 #include "vm_pool.h"
 #include "vm_stack.h"
+#include "logging.h"
 
 #include <stddef.h>
 #include <stdlib.h>
@@ -48,11 +49,14 @@ static struct vm_pool_elem**     fstack;
 static        uint32_t           fstack_len;
 static        uint32_t           fstack_top;
 
+const char* err_stage;
+
 static inline struct vm_pool_elem*
 vm_pool_elem_alloc() {
     struct vm_pool_elem* new_elem;
     if (holes->pos == UINT32_MAX) {
         if (UNLIKELY(++active_pool->pos >= pool_len)) {
+            u6a_err_vm_pool_oom(err_stage);
             return NULL;
         }
         new_elem = active_pool->elems + active_pool->pos;
@@ -89,21 +93,24 @@ free_stack_pop() {
 }
 
 bool
-u6a_vm_pool_init(uint32_t pool_len_, uint32_t ins_len) {
+u6a_vm_pool_init(uint32_t pool_len_, uint32_t ins_len, const char* err_stage_) {
     const uint32_t pool_size = sizeof(struct vm_pool) + pool_len_ * sizeof(struct vm_pool_elem);
     active_pool = malloc(pool_size);
     if (UNLIKELY(active_pool == NULL)) {
+        u6a_err_bad_alloc(err_stage_, pool_size);
         return false;
     }
     const uint32_t holes_size = sizeof(struct vm_pool_elem_ptrs) + pool_len_ * sizeof(struct vm_pool_elem*);
     holes = malloc(holes_size);
     if (UNLIKELY(holes == NULL)) {
+        u6a_err_bad_alloc(err_stage_, holes_size);
         free(holes);
         return false;
     }
     const uint32_t free_stack_size = ins_len * sizeof(struct vm_pool_elem*);
     fstack = malloc(free_stack_size);
     if (UNLIKELY(fstack == NULL)) {
+        u6a_err_bad_alloc(err_stage_, free_stack_size);
         free(active_pool);
         free(holes);
         return false;
@@ -112,6 +119,7 @@ u6a_vm_pool_init(uint32_t pool_len_, uint32_t ins_len) {
     holes->pos = UINT32_MAX;
     pool_len = pool_len_;
     fstack_len = ins_len;
+    err_stage = err_stage_;
     return true;
 }
 
diff --git a/src/vm_pool.h b/src/vm_pool.h
index 701198b..a7d66db 100644
--- a/src/vm_pool.h
+++ b/src/vm_pool.h
@@ -27,7 +27,7 @@
 #include <stdbool.h>
 
 bool
-u6a_vm_pool_init(uint32_t pool_len, uint32_t ins_len);
+u6a_vm_pool_init(uint32_t pool_len, uint32_t ins_len, const char* err_stage);
 
 uint32_t
 u6a_vm_pool_alloc1(struct u6a_vm_var_fn v1);
diff --git a/src/vm_stack.c b/src/vm_stack.c
index 3ff9e2b..78ecff1 100644
--- a/src/vm_stack.c
+++ b/src/vm_stack.c
@@ -19,6 +19,7 @@
 
 #include "vm_stack.h"
 #include "vm_pool.h"
+#include "logging.h"
 
 #include <stddef.h>
 #include <stdlib.h>
@@ -34,11 +35,14 @@ struct vm_stack {
 static struct vm_stack* active_stack;
 static        uint32_t  stack_seg_len;
 
+const char* err_stage;
+
 static inline struct vm_stack*
 vm_stack_create(struct vm_stack* prev, uint32_t top) {
     const uint32_t size = sizeof(struct vm_stack) + stack_seg_len * sizeof(struct u6a_vm_var_fn);
     struct vm_stack* vs = malloc(size);
     if (UNLIKELY(vs == NULL)) {
+        u6a_err_bad_alloc(err_stage, size);
         return NULL;
     }
     vs->prev = prev;
@@ -52,6 +56,7 @@ vm_stack_dup(struct vm_stack* vs) {
     const uint32_t size = sizeof(struct vm_stack) + stack_seg_len * sizeof(struct u6a_vm_var_fn);
     struct vm_stack* dup_stack = malloc(size);
     if (UNLIKELY(dup_stack == NULL)) {
+        u6a_err_bad_alloc(err_stage, size);
         return NULL;
     }
     memcpy(dup_stack, vs, sizeof(struct vm_stack) + (vs->top + 1) * sizeof(struct u6a_vm_var_fn));
@@ -89,9 +94,10 @@ vm_stack_free(struct vm_stack* vs) {
 }
 
 bool
-u6a_vm_stack_init(uint32_t stack_seg_len_) {
+u6a_vm_stack_init(uint32_t stack_seg_len_, const char* err_stage_) {
     active_stack = vm_stack_create(NULL, UINT32_MAX);
     stack_seg_len = stack_seg_len_;
+    err_stage = err_stage_;
     return active_stack != NULL;
 }
 
@@ -198,6 +204,7 @@ u6a_vm_stack_pop() {
     }
     active_stack = vs->prev;
     if (UNLIKELY(active_stack == NULL)) {
+        u6a_err_stack_underflow(err_stage);
         active_stack = vs;
         return false;
     }
diff --git a/src/vm_stack.h b/src/vm_stack.h
index 60ff66e..65bbd53 100644
--- a/src/vm_stack.h
+++ b/src/vm_stack.h
@@ -27,7 +27,7 @@
 #include <stdbool.h>
 
 bool
-u6a_vm_stack_init(uint32_t stack_seg_len);
+u6a_vm_stack_init(uint32_t stack_seg_len, const char* err_stage);
 
 struct u6a_vm_var_fn
 u6a_vm_stack_top();