diff --git a/compiler/rustc_ast_pretty/src/pprust/state.rs b/compiler/rustc_ast_pretty/src/pprust/state.rs
index b80a553b4185ce7f3b551b66c299470c15e83146..ad8dbfd506d212f32d9931d945995a597f0e515d 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state.rs
@@ -814,7 +814,7 @@ fn ty_to_string(&self, ty: &ast::Ty) -> String {
     }
 
     fn bounds_to_string(&self, bounds: &[ast::GenericBound]) -> String {
-        Self::to_string(|s| s.print_type_bounds("", bounds))
+        Self::to_string(|s| s.print_type_bounds(bounds))
     }
 
     fn pat_to_string(&self, pat: &ast::Pat) -> String {
@@ -991,7 +991,12 @@ pub fn print_assoc_constraint(&mut self, constraint: &ast::AssocConstraint) {
                     Term::Const(c) => self.print_expr_anon_const(c, &[]),
                 }
             }
-            ast::AssocConstraintKind::Bound { bounds } => self.print_type_bounds(":", &*bounds),
+            ast::AssocConstraintKind::Bound { bounds } => {
+                if !bounds.is_empty() {
+                    self.word_nbsp(":");
+                    self.print_type_bounds(&bounds);
+                }
+            }
         }
     }
 
@@ -1045,11 +1050,14 @@ pub fn print_type(&mut self, ty: &ast::Ty) {
             }
             ast::TyKind::Path(Some(ref qself), ref path) => self.print_qpath(path, qself, false),
             ast::TyKind::TraitObject(ref bounds, syntax) => {
-                let prefix = if syntax == ast::TraitObjectSyntax::Dyn { "dyn" } else { "" };
-                self.print_type_bounds(prefix, &bounds);
+                if syntax == ast::TraitObjectSyntax::Dyn {
+                    self.word_nbsp("dyn");
+                }
+                self.print_type_bounds(bounds);
             }
             ast::TyKind::ImplTrait(_, ref bounds) => {
-                self.print_type_bounds("impl", &bounds);
+                self.word_nbsp("impl");
+                self.print_type_bounds(bounds);
             }
             ast::TyKind::Array(ref ty, ref length) => {
                 self.word("[");
@@ -1549,29 +1557,24 @@ pub(crate) fn print_asyncness(&mut self, asyncness: ast::Async) {
         }
     }
 
-    pub fn print_type_bounds(&mut self, prefix: &'static str, bounds: &[ast::GenericBound]) {
-        if !bounds.is_empty() {
-            self.word(prefix);
-            let mut first = true;
-            for bound in bounds {
-                if !(first && prefix.is_empty()) {
-                    self.nbsp();
-                }
-                if first {
-                    first = false;
-                } else {
-                    self.word_space("+");
-                }
+    pub fn print_type_bounds(&mut self, bounds: &[ast::GenericBound]) {
+        let mut first = true;
+        for bound in bounds {
+            if first {
+                first = false;
+            } else {
+                self.nbsp();
+                self.word_space("+");
+            }
 
-                match bound {
-                    GenericBound::Trait(tref, modifier) => {
-                        if modifier == &TraitBoundModifier::Maybe {
-                            self.word("?");
-                        }
-                        self.print_poly_trait_ref(tref);
+            match bound {
+                GenericBound::Trait(tref, modifier) => {
+                    if modifier == &TraitBoundModifier::Maybe {
+                        self.word("?");
                     }
-                    GenericBound::Outlives(lt) => self.print_lifetime(*lt),
+                    self.print_poly_trait_ref(tref);
                 }
+                GenericBound::Outlives(lt) => self.print_lifetime(*lt),
             }
         }
     }
@@ -1580,22 +1583,14 @@ pub(crate) fn print_lifetime(&mut self, lifetime: ast::Lifetime) {
         self.print_name(lifetime.ident.name)
     }
 
-    pub(crate) fn print_lifetime_bounds(
-        &mut self,
-        lifetime: ast::Lifetime,
-        bounds: &ast::GenericBounds,
-    ) {
-        self.print_lifetime(lifetime);
-        if !bounds.is_empty() {
-            self.word(": ");
-            for (i, bound) in bounds.iter().enumerate() {
-                if i != 0 {
-                    self.word(" + ");
-                }
-                match bound {
-                    ast::GenericBound::Outlives(lt) => self.print_lifetime(*lt),
-                    _ => panic!(),
-                }
+    pub(crate) fn print_lifetime_bounds(&mut self, bounds: &ast::GenericBounds) {
+        for (i, bound) in bounds.iter().enumerate() {
+            if i != 0 {
+                self.word(" + ");
+            }
+            match bound {
+                ast::GenericBound::Outlives(lt) => self.print_lifetime(*lt),
+                _ => panic!(),
             }
         }
     }
@@ -1613,11 +1608,18 @@ pub(crate) fn print_generic_params(&mut self, generic_params: &[ast::GenericPara
             match param.kind {
                 ast::GenericParamKind::Lifetime => {
                     let lt = ast::Lifetime { id: param.id, ident: param.ident };
-                    s.print_lifetime_bounds(lt, &param.bounds)
+                    s.print_lifetime(lt);
+                    if !param.bounds.is_empty() {
+                        s.word_nbsp(":");
+                        s.print_lifetime_bounds(&param.bounds)
+                    }
                 }
                 ast::GenericParamKind::Type { ref default } => {
                     s.print_ident(param.ident);
-                    s.print_type_bounds(":", &param.bounds);
+                    if !param.bounds.is_empty() {
+                        s.word_nbsp(":");
+                        s.print_type_bounds(&param.bounds);
+                    }
                     if let Some(ref default) = default {
                         s.space();
                         s.word_space("=");
@@ -1630,7 +1632,10 @@ pub(crate) fn print_generic_params(&mut self, generic_params: &[ast::GenericPara
                     s.space();
                     s.word_space(":");
                     s.print_type(ty);
-                    s.print_type_bounds(":", &param.bounds);
+                    if !param.bounds.is_empty() {
+                        s.word_nbsp(":");
+                        s.print_type_bounds(&param.bounds);
+                    }
                     if let Some(ref default) = default {
                         s.space();
                         s.word_space("=");
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/item.rs b/compiler/rustc_ast_pretty/src/pprust/state/item.rs
index 67b539a7ad41b77f25b231fe34c89773704ed1b8..f1caf22f3640fc9ced4e03f4df36e955e1ff58de 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state/item.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state/item.rs
@@ -114,7 +114,10 @@ fn print_associated_type(
         self.word_space("type");
         self.print_ident(ident);
         self.print_generic_params(&generics.params);
-        self.print_type_bounds(":", bounds);
+        if !bounds.is_empty() {
+            self.word_nbsp(":");
+            self.print_type_bounds(bounds);
+        }
         self.print_where_clause_parts(where_clauses.0.0, before_predicates);
         if let Some(ty) = ty {
             self.space();
@@ -320,7 +323,10 @@ pub(crate) fn print_item(&mut self, item: &ast::Item) {
                         real_bounds.push(b.clone());
                     }
                 }
-                self.print_type_bounds(":", &real_bounds);
+                if !real_bounds.is_empty() {
+                    self.word_nbsp(":");
+                    self.print_type_bounds(&real_bounds);
+                }
                 self.print_where_clause(&generics.where_clause);
                 self.word(" ");
                 self.bopen();
@@ -347,7 +353,10 @@ pub(crate) fn print_item(&mut self, item: &ast::Item) {
                     }
                 }
                 self.nbsp();
-                self.print_type_bounds("=", &real_bounds);
+                if !real_bounds.is_empty() {
+                    self.word_nbsp("=");
+                    self.print_type_bounds(&real_bounds);
+                }
                 self.print_where_clause(&generics.where_clause);
                 self.word(";");
                 self.end(); // end inner head-block
@@ -618,14 +627,23 @@ pub fn print_where_predicate(&mut self, predicate: &ast::WherePredicate) {
             }) => {
                 self.print_formal_generic_params(bound_generic_params);
                 self.print_type(bounded_ty);
-                self.print_type_bounds(":", bounds);
+                self.word(":");
+                if !bounds.is_empty() {
+                    self.nbsp();
+                    self.print_type_bounds(bounds);
+                }
             }
             ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
                 lifetime,
                 bounds,
                 ..
             }) => {
-                self.print_lifetime_bounds(*lifetime, bounds);
+                self.print_lifetime(*lifetime);
+                self.word(":");
+                if !bounds.is_empty() {
+                    self.nbsp();
+                    self.print_lifetime_bounds(bounds);
+                }
             }
             ast::WherePredicate::EqPredicate(ast::WhereEqPredicate { lhs_ty, rhs_ty, .. }) => {
                 self.print_type(lhs_ty);
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index acf892cec532871518b6a62f61c588067b215804..ba325d704228da3d92de52cddf0c8b1c08d37774 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -1355,7 +1355,10 @@ pub(super) fn maybe_recover_from_bad_type_plus(&mut self, ty: &Ty) -> PResult<'a
                     s.print_mutability(mut_ty.mutbl, false);
                     s.popen();
                     s.print_type(&mut_ty.ty);
-                    s.print_type_bounds(" +", &bounds);
+                    if !bounds.is_empty() {
+                        s.word(" + ");
+                        s.print_type_bounds(&bounds);
+                    }
                     s.pclose()
                 });
 
diff --git a/src/test/pretty/where-clauses.rs b/src/test/pretty/where-clauses.rs
index 5614a81b0eb410f0d7afe97ed090e244a296428f..4183799457b7fb0c744dc321fed0d1a92ee87185 100644
--- a/src/test/pretty/where-clauses.rs
+++ b/src/test/pretty/where-clauses.rs
@@ -2,4 +2,7 @@
 
 fn f<'a, 'b, T>(t: T) -> isize where T: 'a, 'a: 'b, T: Eq { 0 }
 
+// This is legal syntax, sometimes generated by macros. `where T: $($bound+)*`
+fn zero_bounds<'a, T>() where 'a:, T: {}
+
 fn main() {}