diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index 446a7a135222..84a61641fe5b 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -192,7 +192,7 @@ declare_lint! {
     /// code generation units. Furthermore, different functions could have the
     /// same address after being merged together.
     UNPREDICTABLE_FUNCTION_POINTER_COMPARISONS,
-    Warn,
+    Deny,
     "detects unpredictable function pointer comparisons"
 }
 
diff --git a/tests/ui/lint/fn-ptr-comparisons.rs b/tests/ui/lint/fn-ptr-comparisons.rs
index 7e56a15383b1..e56bc74d90a1 100644
--- a/tests/ui/lint/fn-ptr-comparisons.rs
+++ b/tests/ui/lint/fn-ptr-comparisons.rs
@@ -1,4 +1,4 @@
-// check-pass
+// check-fail
 
 extern "C" {
     fn test();
@@ -14,21 +14,21 @@ fn main() {
     let g: F = f;
 
     let _ = f == a;
-    //~^ WARN function pointer comparisons
+    //~^ ERROR function pointer comparisons
     let _ = f != a;
-    //~^ WARN function pointer comparisons
+    //~^ ERROR function pointer comparisons
     let _ = f == g;
-    //~^ WARN function pointer comparisons
+    //~^ ERROR function pointer comparisons
     let _ = f == f;
-    //~^ WARN function pointer comparisons
+    //~^ ERROR function pointer comparisons
     let _ = g == g;
-    //~^ WARN function pointer comparisons
+    //~^ ERROR function pointer comparisons
 
     let cfn: extern "C" fn() = c;
     let _ = cfn == c;
-    //~^ WARN function pointer comparisons
+    //~^ ERROR function pointer comparisons
 
     let t: unsafe extern "C" fn() = test;
     let _ = t == test;
-    //~^ WARN function pointer comparisons
+    //~^ ERROR function pointer comparisons
 }
diff --git a/tests/ui/lint/fn-ptr-comparisons.stderr b/tests/ui/lint/fn-ptr-comparisons.stderr
index 5b37511ae859..56c6ce7e526c 100644
--- a/tests/ui/lint/fn-ptr-comparisons.stderr
+++ b/tests/ui/lint/fn-ptr-comparisons.stderr
@@ -1,4 +1,4 @@
-warning: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
+error: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
   --> $DIR/fn-ptr-comparisons.rs:16:13
    |
 LL |     let _ = f == a;
@@ -6,9 +6,9 @@ LL |     let _ = f == a;
    |
    = note: the address of the same function can very between different codegen units
    = note: furthermore, different functions could have the same address after being merged together
-   = note: `#[warn(unpredictable_function_pointer_comparisons)]` on by default
+   = note: `#[deny(unpredictable_function_pointer_comparisons)]` on by default
 
-warning: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
+error: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
   --> $DIR/fn-ptr-comparisons.rs:18:13
    |
 LL |     let _ = f != a;
@@ -17,7 +17,7 @@ LL |     let _ = f != a;
    = note: the address of the same function can very between different codegen units
    = note: furthermore, different functions could have the same address after being merged together
 
-warning: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
+error: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
   --> $DIR/fn-ptr-comparisons.rs:20:13
    |
 LL |     let _ = f == g;
@@ -26,7 +26,7 @@ LL |     let _ = f == g;
    = note: the address of the same function can very between different codegen units
    = note: furthermore, different functions could have the same address after being merged together
 
-warning: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
+error: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
   --> $DIR/fn-ptr-comparisons.rs:22:13
    |
 LL |     let _ = f == f;
@@ -35,7 +35,7 @@ LL |     let _ = f == f;
    = note: the address of the same function can very between different codegen units
    = note: furthermore, different functions could have the same address after being merged together
 
-warning: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
+error: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
   --> $DIR/fn-ptr-comparisons.rs:24:13
    |
 LL |     let _ = g == g;
@@ -44,7 +44,7 @@ LL |     let _ = g == g;
    = note: the address of the same function can very between different codegen units
    = note: furthermore, different functions could have the same address after being merged together
 
-warning: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
+error: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
   --> $DIR/fn-ptr-comparisons.rs:28:13
    |
 LL |     let _ = cfn == c;
@@ -53,7 +53,7 @@ LL |     let _ = cfn == c;
    = note: the address of the same function can very between different codegen units
    = note: furthermore, different functions could have the same address after being merged together
 
-warning: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
+error: function pointer comparisons do not produce meaningful results since their addresses are not guaranteed to be unique
   --> $DIR/fn-ptr-comparisons.rs:32:13
    |
 LL |     let _ = t == test;
@@ -62,5 +62,5 @@ LL |     let _ = t == test;
    = note: the address of the same function can very between different codegen units
    = note: furthermore, different functions could have the same address after being merged together
 
-warning: 7 warnings emitted
+error: aborting due to 7 previous errors