diff --git a/src/map.rs b/src/map.rs
index 30c0a4eb57..314a9a1a1a 100644
--- a/src/map.rs
+++ b/src/map.rs
@@ -4132,6 +4132,11 @@ impl<'a, K, V, S, A: Allocator + Clone> RawVacantEntryMut<'a, K, V, S, A> {
             hash_builder: self.hash_builder,
         }
     }
+
+    #[inline]
+    pub(crate) fn hasher(&self) -> &S {
+        self.hash_builder
+    }
 }
 
 impl<K, V, S, A: Allocator + Clone> Debug for RawEntryBuilderMut<'_, K, V, S, A> {
diff --git a/src/set.rs b/src/set.rs
index ce794ce50a..51b73ef348 100644
--- a/src/set.rs
+++ b/src/set.rs
@@ -8,7 +8,10 @@ use core::iter::{Chain, FromIterator, FusedIterator};
 use core::mem;
 use core::ops::{BitAnd, BitOr, BitXor, Sub};
 
-use super::map::{self, ConsumeAllOnDrop, DefaultHashBuilder, DrainFilterInner, HashMap, Keys};
+use super::map::{
+    self, make_hash, make_insert_hash, ConsumeAllOnDrop, DefaultHashBuilder, DrainFilterInner,
+    HashMap, Keys, RawEntryMut,
+};
 use crate::raw::{Allocator, Global};
 
 // Future Optimization (FIXME!)
@@ -953,6 +956,12 @@ where
     /// Inserts a value computed from `f` into the set if the given `value` is
     /// not present, then returns a reference to the value in the set.
     ///
+    /// # Panics
+    ///
+    /// Panics if the value from the function and the provided lookup value
+    /// are not equivalent or have different hashes. See [`Equivalent`]
+    /// and [`Hash`] for more information.
+    ///
     /// # Examples
     ///
     /// ```
@@ -967,6 +976,7 @@ where
     ///     assert_eq!(value, pet);
     /// }
     /// assert_eq!(set.len(), 4); // a new "fish" was inserted
+    /// assert!(set.contains("fish"));
     /// ```
     #[cfg_attr(feature = "inline-more", inline)]
     pub fn get_or_insert_with<Q: ?Sized, F>(&mut self, value: &Q, f: F) -> &T
@@ -974,13 +984,32 @@ where
         Q: Hash + Equivalent<T>,
         F: FnOnce(&Q) -> T,
     {
+        #[cold]
+        #[inline(never)]
+        fn assert_failed() {
+            panic!(
+                "the value from the function and the lookup value \
+                must be equivalent and have the same hash"
+            );
+        }
+
         // Although the raw entry gives us `&mut T`, we only return `&T` to be consistent with
         // `get`. Key mutation is "raw" because you're not supposed to affect `Eq` or `Hash`.
-        self.map
-            .raw_entry_mut()
-            .from_key(value)
-            .or_insert_with(|| (f(value), ()))
-            .0
+        let hash = make_hash::<Q, S>(&self.map.hash_builder, value);
+        let raw_entry_builder = self.map.raw_entry_mut();
+        match raw_entry_builder.from_key_hashed_nocheck(hash, value) {
+            RawEntryMut::Occupied(entry) => entry.into_key(),
+            RawEntryMut::Vacant(entry) => {
+                let insert_value = f(value);
+                let insert_value_hash = make_insert_hash::<T, S>(entry.hasher(), &insert_value);
+                if !(hash == insert_value_hash && value.equivalent(&insert_value)) {
+                    assert_failed();
+                }
+                entry
+                    .insert_hashed_nocheck(insert_value_hash, insert_value, ())
+                    .0
+            }
+        }
     }
 
     /// Gets the given value's corresponding entry in the set for in-place manipulation.
@@ -2429,7 +2458,7 @@ fn assert_covariance() {
 #[cfg(test)]
 mod test_set {
     use super::super::map::DefaultHashBuilder;
-    use super::HashSet;
+    use super::{make_hash, Equivalent, HashSet};
     use std::vec::Vec;
 
     #[test]
@@ -2886,4 +2915,88 @@ mod test_set {
             set.insert(i);
         }
     }
+
+    #[test]
+    fn duplicate_insert() {
+        let mut set = HashSet::new();
+        set.insert(1);
+        set.get_or_insert_with(&1, |_| 1);
+        set.get_or_insert_with(&1, |_| 1);
+        assert!([1].iter().eq(set.iter()));
+    }
+
+    #[test]
+    #[allow(clippy::derived_hash_with_manual_eq)]
+    #[should_panic]
+    fn some_invalid_hash() {
+        use core::hash::{Hash, Hasher};
+        #[derive(Eq, PartialEq)]
+        struct Invalid {
+            count: u32,
+        }
+
+        struct InvalidRef {
+            count: u32,
+        }
+        impl Equivalent<Invalid> for InvalidRef {
+            fn equivalent(&self, key: &Invalid) -> bool {
+                self.count == key.count
+            }
+        }
+        impl Hash for Invalid {
+            fn hash<H: Hasher>(&self, state: &mut H) {
+                self.count.hash(state);
+            }
+        }
+        impl Hash for InvalidRef {
+            fn hash<H: Hasher>(&self, state: &mut H) {
+                let double = self.count * 2;
+                double.hash(state);
+            }
+        }
+        let mut set: HashSet<Invalid> = HashSet::new();
+        let key = InvalidRef { count: 1 };
+        let value = Invalid { count: 1 };
+        if key.equivalent(&value) {
+            set.get_or_insert_with(&key, |_| value);
+        }
+    }
+
+    #[test]
+    #[allow(clippy::derived_hash_with_manual_eq)]
+    #[should_panic]
+    fn some_invalid_equivalent() {
+        use core::hash::{Hash, Hasher};
+        #[derive(Eq, PartialEq)]
+        struct Invalid {
+            count: u32,
+            other: u32,
+        }
+
+        struct InvalidRef {
+            count: u32,
+            other: u32,
+        }
+        impl Equivalent<Invalid> for InvalidRef {
+            fn equivalent(&self, key: &Invalid) -> bool {
+                self.count == key.count && self.other == key.other
+            }
+        }
+        impl Hash for Invalid {
+            fn hash<H: Hasher>(&self, state: &mut H) {
+                self.count.hash(state);
+            }
+        }
+        impl Hash for InvalidRef {
+            fn hash<H: Hasher>(&self, state: &mut H) {
+                self.count.hash(state);
+            }
+        }
+        let mut set: HashSet<Invalid> = HashSet::new();
+        let key = InvalidRef { count: 1, other: 1 };
+        let value = Invalid { count: 1, other: 2 };
+        if make_hash(set.hasher(), &key) == make_hash(set.hasher(), &value) {
+            set.get_or_insert_with(&key, |_| value);
+        }
+    }
 }