diff --git a/packages/@sanity/mutator/src/patch/Patcher.ts b/packages/@sanity/mutator/src/patch/Patcher.ts
index 9db31b203a2..9cc3c4233f7 100644
--- a/packages/@sanity/mutator/src/patch/Patcher.ts
+++ b/packages/@sanity/mutator/src/patch/Patcher.ts
@@ -3,6 +3,8 @@ import {Matcher} from '../jsonpath'
 import {parsePatch} from './parse'
 import {ImmutableAccessor} from './ImmutableAccessor'
 import {PatchTypes, SingleDocumentPatch} from './types'
+import {SetPatch} from './SetPatch'
+import {SetIfMissingPatch} from './SetIfMissingPatch'
 
 export interface Patch {
   id: string
@@ -57,6 +59,9 @@ export class Patcher {
 // a patch to be the payload. When matchers report a delivery, the
 // apply(targets, accessor) is called on the patch
 function process(matcher: Matcher, accessor: ImmutableAccessor) {
+  const isSetPatch =
+    matcher.payload instanceof SetPatch || matcher.payload instanceof SetIfMissingPatch
+
   let result = accessor
   // Every time we execute the matcher a new set of leads is generated. Each lead
   // is a target (being an index, an attribute name or a range) in the form of an
@@ -75,7 +80,20 @@ function process(matcher: Matcher, accessor: ImmutableAccessor) {
         result = result.setIndexAccessor(i, process(lead.matcher, item))
       })
     } else if (lead.target.isAttributeReference()) {
-      const oldValueAccessor = result.getAttribute(lead.target.name())
+      // `set`/`setIfMissing` on a primitive value overwrites it
+      if (isSetPatch && result.containerType() === 'primitive') {
+        result = result.set({})
+      }
+
+      let oldValueAccessor = result.getAttribute(lead.target.name())
+
+      // If the patch is a set/setIfMissing patch, we allow deeply setting properties,
+      // creating missing segments as we go.
+      if (!oldValueAccessor && isSetPatch) {
+        result = result.setAttribute(lead.target.name(), {})
+        oldValueAccessor = result.getAttribute(lead.target.name())
+      }
+
       if (!oldValueAccessor) {
         // Don't follow lead, no such attribute
         return
diff --git a/packages/@sanity/mutator/src/patch/SetIfMissingPatch.ts b/packages/@sanity/mutator/src/patch/SetIfMissingPatch.ts
index 198bb3ba77d..0cf5a529057 100644
--- a/packages/@sanity/mutator/src/patch/SetIfMissingPatch.ts
+++ b/packages/@sanity/mutator/src/patch/SetIfMissingPatch.ts
@@ -16,9 +16,14 @@ export class SetIfMissingPatch {
     let result = accessor
     targets.forEach((target) => {
       if (target.isIndexReference()) {
-        // setIfMissing do not apply to arrays, since Gradient will reject nulls in arrays
+        // setIfMissing do not apply to arrays, since Content Lake will reject nulls in arrays
       } else if (target.isAttributeReference()) {
-        if (!result.hasAttribute(target.name())) {
+        // setting a subproperty on a primitive value overwrites it, eg
+        // `{setIfMissing: {'address.street': 'California St'}}` on `{address: 'Fiction St'}` will
+        // result in `{address: {street: 'California St'}}`
+        if (result.containerType() === 'primitive') {
+          result = result.set({[target.name()]: this.value})
+        } else if (!result.hasAttribute(target.name())) {
           result = accessor.setAttribute(target.name(), this.value)
         }
       } else {
diff --git a/packages/@sanity/mutator/src/patch/SetPatch.ts b/packages/@sanity/mutator/src/patch/SetPatch.ts
index 8e6401ec71b..41bc5fdd326 100644
--- a/packages/@sanity/mutator/src/patch/SetPatch.ts
+++ b/packages/@sanity/mutator/src/patch/SetPatch.ts
@@ -22,7 +22,14 @@ export class SetPatch {
           result = result.setIndex(i, this.value)
         })
       } else if (target.isAttributeReference()) {
-        result = result.setAttribute(target.name(), this.value)
+        // setting a subproperty on a primitive value overwrites it, eg
+        // `{set: {'address.street': 'California St'}}` on `{address: 'Fiction St'}` will result in
+        // `{address: {street: 'California St'}}`
+        if (result.containerType() === 'primitive') {
+          result = result.set({[target.name()]: this.value})
+        } else {
+          result = result.setAttribute(target.name(), this.value)
+        }
       } else {
         throw new Error(`Unable to apply to target ${target.toString()}`)
       }
diff --git a/packages/@sanity/mutator/test/patchExamples/set.ts b/packages/@sanity/mutator/test/patchExamples/set.ts
index 08ff855fe9f..653563f924a 100644
--- a/packages/@sanity/mutator/test/patchExamples/set.ts
+++ b/packages/@sanity/mutator/test/patchExamples/set.ts
@@ -125,6 +125,78 @@ const examples: PatchExample[] = [
       a: 'hello',
     },
   },
+  {
+    name: 'Set new deep key',
+    before: {},
+    patch: {
+      id: 'a',
+      set: {
+        'a.b.c': 'hello',
+      },
+    },
+    after: {
+      a: {
+        b: {
+          c: 'hello',
+        },
+      },
+    },
+  },
+  {
+    name: 'Set deep key on previous string value',
+    before: {
+      a: 'stringValue',
+    },
+    patch: {
+      id: 'a',
+      set: {
+        'a.b.c': 'hello',
+      },
+    },
+    after: {
+      a: {
+        b: {
+          c: 'hello',
+        },
+      },
+    },
+  },
+  {
+    name: 'Set deep key on previous number value',
+    before: {
+      a: 123,
+    },
+    patch: {
+      id: 'a',
+      set: {
+        'a.b.c': 'hello',
+      },
+    },
+    after: {
+      a: {
+        b: {
+          c: 'hello',
+        },
+      },
+    },
+  },
+  {
+    name: 'Set key on previous number value',
+    before: {
+      a: 123,
+    },
+    patch: {
+      id: 'a',
+      set: {
+        'a.b': 'hello',
+      },
+    },
+    after: {
+      a: {
+        b: 'hello',
+      },
+    },
+  },
   {
     name: 'Set range',
     before: {
diff --git a/packages/@sanity/mutator/test/patchExamples/setIfMissing.ts b/packages/@sanity/mutator/test/patchExamples/setIfMissing.ts
index 4de83eba82a..7dc7cf532e1 100644
--- a/packages/@sanity/mutator/test/patchExamples/setIfMissing.ts
+++ b/packages/@sanity/mutator/test/patchExamples/setIfMissing.ts
@@ -60,7 +60,80 @@ const examples: PatchExample[] = [
         {b: 7, p: 'Thorvald Meyers gt.', zz: {yyy: 55, zzz: 10}},
       ],
     },
-  }, // Potentially redundant, added to exactly match a test case from @sanity/form-builder that was failing.
+  },
+  {
+    name: 'Set new deep key',
+    before: {},
+    patch: {
+      id: 'a',
+      setIfMissing: {
+        'a.b.c': 'hello',
+      },
+    },
+    after: {
+      a: {
+        b: {
+          c: 'hello',
+        },
+      },
+    },
+  },
+  {
+    name: 'Set deep key on previous string value',
+    before: {
+      a: 'stringValue',
+    },
+    patch: {
+      id: 'a',
+      setIfMissing: {
+        'a.b.c': 'hello',
+      },
+    },
+    after: {
+      a: {
+        b: {
+          c: 'hello',
+        },
+      },
+    },
+  },
+  {
+    name: 'Set deep key on previous number value',
+    before: {
+      a: 123,
+    },
+    patch: {
+      id: 'a',
+      setIfMissing: {
+        'a.b.c': 'hello',
+      },
+    },
+    after: {
+      a: {
+        b: {
+          c: 'hello',
+        },
+      },
+    },
+  },
+  {
+    name: 'Set key on previous number value',
+    before: {
+      a: 123,
+    },
+    patch: {
+      id: 'a',
+      setIfMissing: {
+        'a.b': 'hello',
+      },
+    },
+    after: {
+      a: {
+        b: 'hello',
+      },
+    },
+  },
+  // Potentially redundant, added to exactly match a test case from @sanity/form-builder that was failing.
   {
     name: 'Set if missing by key',
     before: {