diff --git a/src/etc/errorck.py b/src/etc/errorck.py
index 48736542f20c7..1b15d2c8598e5 100644
--- a/src/etc/errorck.py
+++ b/src/etc/errorck.py
@@ -21,8 +21,31 @@
 
 src_dir = sys.argv[1]
 errcode_map = {}
+errcode_checked = []
+errcode_not_found = []
 error_re = re.compile("(E\d\d\d\d)")
 
+def check_unused_error_codes(error_codes, check_error_codes, filenames, dirnames, dirpath):
+    for filename in filenames:
+        if filename == "diagnostics.rs" or not filename.endswith(".rs"):
+            continue
+        path = os.path.join(dirpath, filename)
+
+        with open(path, 'r') as f:
+            for line in f:
+                match = error_re.search(line)
+                if match:
+                    errcode = match.group(1)
+                    if errcode in error_codes:
+                        error_codes.remove(errcode)
+                    if errcode not in check_error_codes:
+                        check_error_codes.append(errcode)
+    for dirname in dirnames:
+        path = os.path.join(dirpath, dirname)
+        for (dirpath, dnames, fnames) in os.walk(path):
+            check_unused_error_codes(error_codes, check_error_codes, fnames, dnames, dirpath)
+
+
 # In the register_long_diagnostics! macro, entries look like this:
 #
 # EXXXX: r##"
@@ -35,19 +58,23 @@
 long_diag_begin = "r##\""
 long_diag_end = "\"##"
 
+errors = False
+all_errors = []
+
 for (dirpath, dirnames, filenames) in os.walk(src_dir):
     if "src/test" in dirpath or "src/llvm" in dirpath:
         # Short circuit for fast
         continue
 
+    errcode_to_check = []
     for filename in filenames:
         if filename != "diagnostics.rs":
             continue
-
         path = os.path.join(dirpath, filename)
 
         with open(path, 'r') as f:
             inside_long_diag = False
+            errcode_to_check = []
             for line_num, line in enumerate(f, start=1):
                 if inside_long_diag:
                     # Skip duplicate error code checking for this line
@@ -65,16 +92,36 @@
                         errcode_map[errcode] = existing + new_record
                     else:
                         errcode_map[errcode] = new_record
+                        # we don't check if this is a long error explanation
+                        if (long_diag_begin not in line and not line.strip().startswith("//")
+                            and errcode not in errcode_to_check and errcode not in errcode_checked
+                            and errcode not in errcode_not_found):
+                            errcode_to_check.append(errcode)
 
                 if long_diag_begin in line:
                     inside_long_diag = True
+        break
+    check_unused_error_codes(errcode_to_check, errcode_checked, filenames, dirnames, dirpath)
+    if len(errcode_to_check) > 0:
+        for errcode in errcode_to_check:
+            if errcode in errcode_checked:
+                continue
+            errcode_not_found.append(errcode)
+
+if len(errcode_not_found) > 0:
+    errcode_not_found.sort()
+    for errcode in errcode_not_found:
+        if errcode in errcode_checked:
+            continue
+        all_errors.append(errcode)
+        print("error: unused error code: " + errcode)
+        errors = True
 
-errors = False
-all_errors = []
 
 for errcode, entries in errcode_map.items():
     all_errors.append(entries[0][0])
     if len(entries) > 1:
+        entries.sort()
         print("error: duplicate error code " + errcode)
         for entry in entries:
             print("{1}: {2}\n{3}".format(*entry))
diff --git a/src/librustc/diagnostics.rs b/src/librustc/diagnostics.rs
index e5942e64a9e40..9dbc75b960ef9 100644
--- a/src/librustc/diagnostics.rs
+++ b/src/librustc/diagnostics.rs
@@ -226,7 +226,7 @@ const X: i32 = 42 / 0;
 ```
 "##,
 
-E0038: r####"
+E0038: r##"
 Trait objects like `Box<Trait>` can only be constructed when certain
 requirements are satisfied by the trait in question.
 
@@ -478,7 +478,7 @@ so they are forbidden when specifying supertraits.
 
 There's no easy fix for this, generally code will need to be refactored so that
 you no longer need to derive from `Super<Self>`.
-"####,
+"##,
 
 E0072: r##"
 When defining a recursive struct or enum, any use of the type being defined
@@ -1801,14 +1801,14 @@ attribute.
 
 
 register_diagnostics! {
-    // E0006 // merged with E0005
+//  E0006 // merged with E0005
 //  E0134,
 //  E0135,
     E0278, // requirement is not satisfied
     E0279, // requirement is not satisfied
     E0280, // requirement is not satisfied
     E0284, // cannot resolve type
-    E0285, // overflow evaluation builtin bounds
+//  E0285, // overflow evaluation builtin bounds
     E0298, // mismatched types between arms
     E0299, // mismatched types between arms
     // E0300, // unexpanded macro
diff --git a/src/librustc_resolve/diagnostics.rs b/src/librustc_resolve/diagnostics.rs
index dc6da1f0ef847..16bcf84b7950e 100644
--- a/src/librustc_resolve/diagnostics.rs
+++ b/src/librustc_resolve/diagnostics.rs
@@ -1046,8 +1046,8 @@ register_diagnostics! {
 //  E0153, unused error code
 //  E0157, unused error code
     E0254, // import conflicts with imported crate in this module
-    E0257,
-    E0258,
+//  E0257,
+//  E0258,
     E0402, // cannot use an outer type parameter in this context
     E0406, // undeclared associated type
     E0408, // variable from pattern #1 is not bound in pattern #