diff --git a/morphisms/digit.morphism-base b/morphisms/digit.morphism-base
index 54b9d9f..97d3bd9 100644
--- a/morphisms/digit.morphism-base
+++ b/morphisms/digit.morphism-base
@@ -1,4 +1,5 @@
 ```
+#include <stdio.h>
 ```
 
 morph_digit_as_char_to_uint8 (Radix:ℤ)
@@ -17,6 +18,7 @@ morph_digit_as_char_to_uint8 (Radix:ℤ)
     if( *dst < Radix ) {
         return 0;
     } else {
+        fprintf(stderr, "digit %u is out of range for radix %u\n", *dst, Radix);
         return -1;
     }
 ```
@@ -37,6 +39,7 @@ morph_digit_as_char_to_uint64 (Radix:ℤ)
     if( *dst < Radix ) {
         return 0;
     } else {
+        fprintf(stderr, "digit %u is out of range for radix %u\n", *dst, Radix);
         return -1;
     }
 ```
@@ -49,8 +52,10 @@ morph_digit_as_uint8_to_char (Radix:ℤ_16)
         *dst = *src + '0';
     else if( *dst < 16 )
         *dst = *src - 0xa + 'a';
-    else
+    else {
+        fprintf(stderr, "digit %u is out of rage for char\n", *dst);
         return -1;
+    }
 
     return 0;
 ```
@@ -63,8 +68,10 @@ morph_digit_as_uint64_to_char (Radix:ℤ_16)
         *dst = *src + '0';
     else if( *dst < 16 )
         *dst = *src - 0xa + 'a';
-    else
+    else {
+        fprintf(stderr, "digit %u is out of rage for char\n", *dst);
         return -1;
+    }
 
     return 0;
 ```
diff --git a/morphisms/length_prefix.morphism-base b/morphisms/length_prefix.morphism-base
index f8b48aa..92cb803 100644
--- a/morphisms/length_prefix.morphism-base
+++ b/morphisms/length_prefix.morphism-base
@@ -1,4 +1,5 @@
 ```
+#include <stdio.h>
 #include <array/length-prefix.h>
 ```
 
diff --git a/morphisms/unicode.morphism-base b/morphisms/unicode.morphism-base
index 8805ace..db4b342 100644
--- a/morphisms/unicode.morphism-base
+++ b/morphisms/unicode.morphism-base
@@ -1,4 +1,5 @@
 ```
+#include <stdio.h>
 ```
 
 morph_string_as_ascii_to_utf8 ()