diff --git a/docs/src/pages/reference/QueryClient.md b/docs/src/pages/reference/QueryClient.md
index b195e050d0..7aad8ff00a 100644
--- a/docs/src/pages/reference/QueryClient.md
+++ b/docs/src/pages/reference/QueryClient.md
@@ -474,6 +474,9 @@ The `getQueryDefaults` method returns the default options which have been set fo
 const defaultOptions = queryClient.getQueryDefaults(['posts'])
 ```
 
+> Note that if several query defaults match the given query key, the **first** matching one is returned.
+> This could lead to unexpected behaviours. See [`setQueryDefaults`](#queryclientsetquerydefaults).
+
 ## `queryClient.setQueryDefaults`
 
 `setQueryDefaults` can be used to set default options for specific queries:
@@ -491,6 +494,9 @@ function Component() {
 - `queryKey: QueryKey`: [Query Keys](../guides/query-keys)
 - `options: QueryOptions`
 
+> As stated in [`getQueryDefaults`](#queryclientgetquerydefaults), the order of registration of query defaults does matter.
+> Since the **first** matching defaults are returned by `getQueryDefaults`, the registration should be made in the following order: from the **least generic key** to the **most generic one**. This way, in case of specific key, the first matching one would be the expected one.
+
 ## `queryClient.getMutationDefaults`
 
 The `getMutationDefaults` method returns the default options which have been set for specific mutations:
@@ -516,6 +522,8 @@ function Component() {
 - `mutationKey: string | unknown[]`
 - `options: MutationOptions`
 
+> Similar to [`setQueryDefaults`](#queryclientsetquerydefaults), the order of registration does matter here.
+
 ## `queryClient.getQueryCache`
 
 The `getQueryCache` method returns the query cache this client is connected to.
diff --git a/src/core/queryClient.ts b/src/core/queryClient.ts
index 7e2fbc02ab..d09461ef83 100644
--- a/src/core/queryClient.ts
+++ b/src/core/queryClient.ts
@@ -38,6 +38,7 @@ import { onlineManager } from './onlineManager'
 import { notifyManager } from './notifyManager'
 import { infiniteQueryBehavior } from './infiniteQueryBehavior'
 import { CancelOptions, DefaultedQueryObserverOptions } from './types'
+import { getLogger } from './logger'
 
 // TYPES
 
@@ -535,10 +536,32 @@ export class QueryClient {
   getQueryDefaults(
     queryKey?: QueryKey
   ): QueryObserverOptions<any, any, any, any, any> | undefined {
-    return queryKey
-      ? this.queryDefaults.find(x => partialMatchKey(queryKey, x.queryKey))
-          ?.defaultOptions
-      : undefined
+    if (!queryKey) {
+      return undefined
+    }
+
+    // Get the first matching defaults
+    const firstMatchingDefaults = this.queryDefaults.find(x =>
+      partialMatchKey(queryKey, x.queryKey)
+    )
+
+    // Additional checks and error in dev mode
+    if (process.env.NODE_ENV !== 'production') {
+      // Retrieve all matching defaults for the given key
+      const matchingDefaults = this.queryDefaults.filter(x =>
+        partialMatchKey(queryKey, x.queryKey)
+      )
+      // It is ok not having defaults, but it is error prone to have more than 1 default for a given key
+      if (matchingDefaults.length > 1) {
+        getLogger().error(
+          `[QueryClient] Several query defaults match with key '${JSON.stringify(
+            queryKey
+          )}'. The first matching query defaults are used. Please check how query defaults are registered. Order does matter here. cf. https://react-query.tanstack.com/reference/QueryClient#queryclientsetquerydefaults.`
+        )
+      }
+    }
+
+    return firstMatchingDefaults?.defaultOptions
   }
 
   setMutationDefaults(
@@ -558,11 +581,32 @@ export class QueryClient {
   getMutationDefaults(
     mutationKey?: MutationKey
   ): MutationObserverOptions<any, any, any, any> | undefined {
-    return mutationKey
-      ? this.mutationDefaults.find(x =>
-          partialMatchKey(mutationKey, x.mutationKey)
-        )?.defaultOptions
-      : undefined
+    if (!mutationKey) {
+      return undefined
+    }
+
+    // Get the first matching defaults
+    const firstMatchingDefaults = this.mutationDefaults.find(x =>
+      partialMatchKey(mutationKey, x.mutationKey)
+    )
+
+    // Additional checks and error in dev mode
+    if (process.env.NODE_ENV !== 'production') {
+      // Retrieve all matching defaults for the given key
+      const matchingDefaults = this.mutationDefaults.filter(x =>
+        partialMatchKey(mutationKey, x.mutationKey)
+      )
+      // It is ok not having defaults, but it is error prone to have more than 1 default for a given key
+      if (matchingDefaults.length > 1) {
+        getLogger().error(
+          `[QueryClient] Several mutation defaults match with key '${JSON.stringify(
+            mutationKey
+          )}'. The first matching mutation defaults are used. Please check how mutation defaults are registered. Order does matter here. cf. https://react-query.tanstack.com/reference/QueryClient#queryclientsetmutationdefaults.`
+        )
+      }
+    }
+
+    return firstMatchingDefaults?.defaultOptions
   }
 
   defaultQueryOptions<
diff --git a/src/core/tests/queryClient.test.tsx b/src/core/tests/queryClient.test.tsx
index 0331415032..c32cf97cc0 100644
--- a/src/core/tests/queryClient.test.tsx
+++ b/src/core/tests/queryClient.test.tsx
@@ -130,6 +130,132 @@ describe('queryClient', () => {
       queryClient.setQueryDefaults(key, queryOptions2)
       expect(queryClient.getQueryDefaults(key)).toMatchObject(queryOptions2)
     })
+
+    test('should warn in dev if several query defaults match a given key', () => {
+      // Check discussion here: https://github.com/tannerlinsley/react-query/discussions/3199
+      const consoleErrorMock = jest.spyOn(console, 'error')
+      consoleErrorMock.mockImplementation(() => true)
+
+      const keyABCD = [
+        {
+          a: 'a',
+          b: 'b',
+          c: 'c',
+          d: 'd',
+        },
+      ]
+
+      // The key below "contains" keyABCD => it is more generic
+      const keyABC = [
+        {
+          a: 'a',
+          b: 'b',
+          c: 'c',
+        },
+      ]
+
+      // The defaults for query matching key "ABCD" (least generic)
+      const defaultsOfABCD = {
+        queryFn: function ABCDQueryFn() {
+          return 'ABCD'
+        },
+      }
+
+      // The defaults for query matching key "ABC" (most generic)
+      const defaultsOfABC = {
+        queryFn: function ABCQueryFn() {
+          return 'ABC'
+        },
+      }
+
+      // No defaults, no warning
+      const noDefaults = queryClient.getQueryDefaults(keyABCD)
+      expect(noDefaults).toBeUndefined()
+      expect(consoleErrorMock).not.toHaveBeenCalled()
+
+      // If defaults for key ABCD are registered **before** the ones of key ABC (more generic)…
+      queryClient.setQueryDefaults(keyABCD, defaultsOfABCD)
+      queryClient.setQueryDefaults(keyABC, defaultsOfABC)
+      // … then the "good" defaults are retrieved: we get the ones for key "ABCD"
+      const goodDefaults = queryClient.getQueryDefaults(keyABCD)
+      expect(goodDefaults).toBe(defaultsOfABCD)
+      // The warning is still raised since several defaults are matching
+      expect(consoleErrorMock).toHaveBeenCalledTimes(1)
+
+      // Let's create another queryClient and change the order of registration
+      const newQueryClient = new QueryClient()
+      // The defaults for key ABC (more generic) are registered **before** the ones of key ABCD…
+      newQueryClient.setQueryDefaults(keyABC, defaultsOfABC)
+      newQueryClient.setQueryDefaults(keyABCD, defaultsOfABCD)
+      // … then the "wrong" defaults are retrieved: we get the ones for key "ABC"
+      const badDefaults = newQueryClient.getQueryDefaults(keyABCD)
+      expect(badDefaults).not.toBe(defaultsOfABCD)
+      expect(badDefaults).toBe(defaultsOfABC)
+      expect(consoleErrorMock).toHaveBeenCalledTimes(2)
+
+      consoleErrorMock.mockRestore()
+    })
+
+    test('should warn in dev if several mutation defaults match a given key', () => {
+      // Check discussion here: https://github.com/tannerlinsley/react-query/discussions/3199
+      const consoleErrorMock = jest.spyOn(console, 'error')
+      consoleErrorMock.mockImplementation(() => true)
+
+      const keyABCD = [
+        {
+          a: 'a',
+          b: 'b',
+          c: 'c',
+          d: 'd',
+        },
+      ]
+
+      // The key below "contains" keyABCD => it is more generic
+      const keyABC = [
+        {
+          a: 'a',
+          b: 'b',
+          c: 'c',
+        },
+      ]
+
+      // The defaults for mutation matching key "ABCD" (least generic)
+      const defaultsOfABCD = {
+        mutationFn: Promise.resolve,
+      }
+
+      // The defaults for mutation matching key "ABC" (most generic)
+      const defaultsOfABC = {
+        mutationFn: Promise.resolve,
+      }
+
+      // No defaults, no warning
+      const noDefaults = queryClient.getMutationDefaults(keyABCD)
+      expect(noDefaults).toBeUndefined()
+      expect(consoleErrorMock).not.toHaveBeenCalled()
+
+      // If defaults for key ABCD are registered **before** the ones of key ABC (more generic)…
+      queryClient.setMutationDefaults(keyABCD, defaultsOfABCD)
+      queryClient.setMutationDefaults(keyABC, defaultsOfABC)
+      // … then the "good" defaults are retrieved: we get the ones for key "ABCD"
+      const goodDefaults = queryClient.getMutationDefaults(keyABCD)
+      expect(goodDefaults).toBe(defaultsOfABCD)
+      // The warning is still raised since several defaults are matching
+      expect(consoleErrorMock).toHaveBeenCalledTimes(1)
+
+      // Let's create another queryClient and change the order of registration
+      const newQueryClient = new QueryClient()
+      // The defaults for key ABC (more generic) are registered **before** the ones of key ABCD…
+      newQueryClient.setMutationDefaults(keyABC, defaultsOfABC)
+      newQueryClient.setMutationDefaults(keyABCD, defaultsOfABCD)
+      // … then the "wrong" defaults are retrieved: we get the ones for key "ABC"
+      const badDefaults = newQueryClient.getMutationDefaults(keyABCD)
+      expect(badDefaults).not.toBe(defaultsOfABCD)
+      expect(badDefaults).toBe(defaultsOfABC)
+      expect(consoleErrorMock).toHaveBeenCalledTimes(2)
+
+      consoleErrorMock.mockRestore()
+    })
   })
 
   describe('setQueryData', () => {