diff --git a/src/librustc_errors/diagnostic.rs b/src/librustc_errors/diagnostic.rs
index 40e4efb397d..bfeb351f1a4 100644
--- a/src/librustc_errors/diagnostic.rs
+++ b/src/librustc_errors/diagnostic.rs
@@ -11,6 +11,7 @@
 use CodeSuggestion;
 use SubstitutionPart;
 use Substitution;
+use SuggestionApproximate;
 use Level;
 use std::fmt;
 use syntax_pos::{MultiSpan, Span};
@@ -222,7 +223,7 @@ impl Diagnostic {
             }],
             msg: msg.to_owned(),
             show_code_when_inline: false,
-            approximate: false,
+            approximate: SuggestionApproximate::Unspecified,
         });
         self
     }
@@ -253,7 +254,7 @@ impl Diagnostic {
             }],
             msg: msg.to_owned(),
             show_code_when_inline: true,
-            approximate: false,
+            approximate: SuggestionApproximate::Unspecified,
         });
         self
     }
@@ -269,7 +270,7 @@ impl Diagnostic {
             }).collect(),
             msg: msg.to_owned(),
             show_code_when_inline: true,
-            approximate: false,
+            approximate: SuggestionApproximate::Unspecified,
         });
         self
     }
@@ -277,7 +278,8 @@ impl Diagnostic {
     /// This is a suggestion that may contain mistakes or fillers and should
     /// be read and understood by a human.
     pub fn span_approximate_suggestion(&mut self, sp: Span, msg: &str,
-                                       suggestion: String) -> &mut Self {
+                                       suggestion: String,
+                                       approximate: SuggestionApproximate) -> &mut Self {
         self.suggestions.push(CodeSuggestion {
             substitutions: vec![Substitution {
                 parts: vec![SubstitutionPart {
@@ -287,13 +289,14 @@ impl Diagnostic {
             }],
             msg: msg.to_owned(),
             show_code_when_inline: true,
-            approximate: true,
+            approximate,
         });
         self
     }
 
     pub fn span_approximate_suggestions(&mut self, sp: Span, msg: &str,
-                                        suggestions: Vec<String>) -> &mut Self {
+                                        suggestions: Vec<String>,
+                                        approximate: SuggestionApproximate) -> &mut Self {
         self.suggestions.push(CodeSuggestion {
             substitutions: suggestions.into_iter().map(|snippet| Substitution {
                 parts: vec![SubstitutionPart {
@@ -303,7 +306,7 @@ impl Diagnostic {
             }).collect(),
             msg: msg.to_owned(),
             show_code_when_inline: true,
-            approximate: true,
+            approximate,
         });
         self
     }
diff --git a/src/librustc_errors/diagnostic_builder.rs b/src/librustc_errors/diagnostic_builder.rs
index 945ecce7ab3..31eacb527ee 100644
--- a/src/librustc_errors/diagnostic_builder.rs
+++ b/src/librustc_errors/diagnostic_builder.rs
@@ -11,6 +11,7 @@
 use Diagnostic;
 use DiagnosticId;
 use DiagnosticStyledString;
+use SuggestionApproximate;
 
 use Level;
 use Handler;
@@ -190,12 +191,14 @@ impl<'a> DiagnosticBuilder<'a> {
     forward!(pub fn span_approximate_suggestion(&mut self,
                                                 sp: Span,
                                                 msg: &str,
-                                                suggestion: String)
+                                                suggestion: String,
+                                                approximate: SuggestionApproximate)
                                                 -> &mut Self);
     forward!(pub fn span_approximate_suggestions(&mut self,
                                                  sp: Span,
                                                  msg: &str,
-                                                 suggestions: Vec<String>)
+                                                 suggestions: Vec<String>,
+                                                 approximate: SuggestionApproximate)
                                                  -> &mut Self);
     forward!(pub fn set_span<S: Into<MultiSpan>>(&mut self, sp: S) -> &mut Self);
     forward!(pub fn code(&mut self, s: DiagnosticId) -> &mut Self);
diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index ce3efef08cc..9abb5b38c05 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -56,6 +56,14 @@ mod lock;
 
 use syntax_pos::{BytePos, Loc, FileLinesResult, FileMap, FileName, MultiSpan, Span, NO_EXPANSION};
 
+#[derive(Copy, Clone, Debug, PartialEq, Hash, RustcEncodable, RustcDecodable)]
+pub enum SuggestionApproximate {
+    MachineApplicable,
+    HasPlaceholders,
+    MaybeIncorrect,
+    Unspecified
+}
+
 #[derive(Clone, Debug, PartialEq, Hash, RustcEncodable, RustcDecodable)]
 pub struct CodeSuggestion {
     /// Each substitute can have multiple variants due to multiple
@@ -87,7 +95,7 @@ pub struct CodeSuggestion {
     /// Sometimes we may show suggestions with placeholders,
     /// which are useful for users but not useful for
     /// tools like rustfix
-    pub approximate: bool,
+    pub approximate: SuggestionApproximate,
 }
 
 #[derive(Clone, Debug, PartialEq, Hash, RustcEncodable, RustcDecodable)]
diff --git a/src/libsyntax/json.rs b/src/libsyntax/json.rs
index b4f34fb12e3..dd77e441499 100644
--- a/src/libsyntax/json.rs
+++ b/src/libsyntax/json.rs
@@ -23,7 +23,7 @@ use codemap::{CodeMap, FilePathMapping};
 use syntax_pos::{self, MacroBacktrace, Span, SpanLabel, MultiSpan};
 use errors::registry::Registry;
 use errors::{DiagnosticBuilder, SubDiagnostic, CodeSuggestion, CodeMapper};
-use errors::DiagnosticId;
+use errors::{DiagnosticId, SuggestionApproximate};
 use errors::emitter::{Emitter, EmitterWriter};
 
 use rustc_data_structures::sync::{self, Lrc};
@@ -138,7 +138,7 @@ struct DiagnosticSpan {
     suggested_replacement: Option<String>,
     /// If the suggestion is approximate
     #[rustc_serialize_exclude_null]
-    suggestion_approximate: Option<bool>,
+    suggestion_approximate: Option<SuggestionApproximate>,
     /// Macro invocations that created the code at this span, if any.
     expansion: Option<Box<DiagnosticSpanMacroExpansion>>,
 }
@@ -239,7 +239,7 @@ impl Diagnostic {
 
 impl DiagnosticSpan {
     fn from_span_label(span: SpanLabel,
-                       suggestion: Option<(&String, bool)>,
+                       suggestion: Option<(&String, SuggestionApproximate)>,
                        je: &JsonEmitter)
                        -> DiagnosticSpan {
         Self::from_span_etc(span.span,
@@ -252,7 +252,7 @@ impl DiagnosticSpan {
     fn from_span_etc(span: Span,
                      is_primary: bool,
                      label: Option<String>,
-                     suggestion: Option<(&String, bool)>,
+                     suggestion: Option<(&String, SuggestionApproximate)>,
                      je: &JsonEmitter)
                      -> DiagnosticSpan {
         // obtain the full backtrace from the `macro_backtrace`
@@ -272,7 +272,7 @@ impl DiagnosticSpan {
     fn from_span_full(span: Span,
                       is_primary: bool,
                       label: Option<String>,
-                      suggestion: Option<(&String, bool)>,
+                      suggestion: Option<(&String, SuggestionApproximate)>,
                       mut backtrace: vec::IntoIter<MacroBacktrace>,
                       je: &JsonEmitter)
                       -> DiagnosticSpan {