diff --git a/src/librustc_error_codes/error_codes.rs b/src/librustc_error_codes/error_codes.rs
index 91a7b6c895838..89359bb1bfdff 100644
--- a/src/librustc_error_codes/error_codes.rs
+++ b/src/librustc_error_codes/error_codes.rs
@@ -418,6 +418,7 @@ E0744: include_str!("./error_codes/E0744.md"),
 E0745: include_str!("./error_codes/E0745.md"),
 E0746: include_str!("./error_codes/E0746.md"),
 E0747: include_str!("./error_codes/E0747.md"),
+E0748: include_str!("./error_codes/E0748.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard
diff --git a/src/librustc_error_codes/error_codes/E0748.md b/src/librustc_error_codes/error_codes/E0748.md
new file mode 100644
index 0000000000000..69f1c026125bf
--- /dev/null
+++ b/src/librustc_error_codes/error_codes/E0748.md
@@ -0,0 +1,16 @@
+A raw string isn't correctly terminated because the trailing `#` count doesn't
+match its leading `#` count.
+
+Erroneous code example:
+
+```compile_fail,E0748
+let dolphins = r##"Dolphins!"#; // error!
+```
+
+To terminate a raw string, you have to have the same number of `#` at the end
+as at the beginning. Example:
+
+```
+let dolphins = r#"Dolphins!"#; // One `#` at the beginning, one at the end so
+                               // all good!
+```
diff --git a/src/librustc_parse/lexer/mod.rs b/src/librustc_parse/lexer/mod.rs
index 66280638a2d40..face0e679927c 100644
--- a/src/librustc_parse/lexer/mod.rs
+++ b/src/librustc_parse/lexer/mod.rs
@@ -1,5 +1,5 @@
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{DiagnosticBuilder, FatalError};
+use rustc_errors::{error_code, DiagnosticBuilder, FatalError};
 use rustc_lexer::unescape;
 use rustc_lexer::Base;
 use rustc_session::parse::ParseSess;
@@ -495,7 +495,11 @@ impl<'a> StringReader<'a> {
     }
 
     fn report_unterminated_raw_string(&self, start: BytePos, n_hashes: usize) -> ! {
-        let mut err = self.struct_span_fatal(start, start, "unterminated raw string");
+        let mut err = self.sess.span_diagnostic.struct_span_fatal_with_code(
+            self.mk_sp(start, start),
+            "unterminated raw string",
+            error_code!(E0748),
+        );
         err.span_label(self.mk_sp(start, start), "unterminated raw string");
 
         if n_hashes > 0 {
diff --git a/src/test/ui/parser/raw-byte-string-eof.stderr b/src/test/ui/parser/raw-byte-string-eof.stderr
index 65fa89f2a81ac..d5f22e2a1a814 100644
--- a/src/test/ui/parser/raw-byte-string-eof.stderr
+++ b/src/test/ui/parser/raw-byte-string-eof.stderr
@@ -1,4 +1,4 @@
-error: unterminated raw string
+error[E0748]: unterminated raw string
   --> $DIR/raw-byte-string-eof.rs:2:5
    |
 LL |     br##"a"#;
@@ -8,3 +8,4 @@ LL |     br##"a"#;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0748`.
diff --git a/src/test/ui/parser/raw-str-unterminated.stderr b/src/test/ui/parser/raw-str-unterminated.stderr
index 67792eb91e5ca..077f763f154c5 100644
--- a/src/test/ui/parser/raw-str-unterminated.stderr
+++ b/src/test/ui/parser/raw-str-unterminated.stderr
@@ -1,4 +1,4 @@
-error: unterminated raw string
+error[E0748]: unterminated raw string
   --> $DIR/raw-str-unterminated.rs:2:5
    |
 LL |     r#" string literal goes on
@@ -8,3 +8,4 @@ LL |     r#" string literal goes on
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0748`.
diff --git a/src/test/ui/parser/raw/raw_string.stderr b/src/test/ui/parser/raw/raw_string.stderr
index 5572511881d57..0f1d7e4651deb 100644
--- a/src/test/ui/parser/raw/raw_string.stderr
+++ b/src/test/ui/parser/raw/raw_string.stderr
@@ -1,4 +1,4 @@
-error: unterminated raw string
+error[E0748]: unterminated raw string
   --> $DIR/raw_string.rs:2:13
    |
 LL |     let x = r##"lol"#;
@@ -8,3 +8,4 @@ LL |     let x = r##"lol"#;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0748`.