diff --git a/std/jule/build/log.jule b/std/jule/build/log.jule
index f71882386..e4891f988 100644
--- a/std/jule/build/log.jule
+++ b/std/jule/build/log.jule
@@ -239,6 +239,7 @@ enum LogMsg: str {
     ArraySizeOverflow: "array with size @ overflows limit (@) of the system",
     InvalidTypeForTypeOf: "comptime::TypeOf is not supports type @",
     ComptimeAsExpr: "compile-time evaluations cannot used as expression",
+    InvalidTypeForFn: `type @ is invalid for function @`,
 
     // Suggestions.
     ExpectedIdentifier: `write an identifier because identifier expected`,
diff --git a/std/jule/sema/builtin.jule b/std/jule/sema/builtin.jule
index cb2bde337..f83151229 100644
--- a/std/jule/sema/builtin.jule
+++ b/std/jule/sema/builtin.jule
@@ -852,6 +852,9 @@ fn builtinCallerStdMemSizeOf(mut &e: &Eval, mut &fc: &FnCallExpr, mut &_: &Data)
     if d == nil {
         ret result
     }
+    if !validTypeForXof(d.Kind) {
+        e.pushErr(fc.Args[0].Token, LogMsg.InvalidTypeForFn, d.Kind.Str(), "SizeOf")
+    }
 
     result.Model = &SizeofExprModel{Expr: d.Model}
     ret result
@@ -874,6 +877,9 @@ fn builtinCallerStdMemAlignOf(mut &e: &Eval, mut &fc: &FnCallExpr, mut &_: &Data
     if d == nil {
         ret result
     }
+    if !validTypeForXof(d.Kind) {
+        e.pushErr(fc.Args[0].Token, LogMsg.InvalidTypeForFn, d.Kind.Str(), "AlignOf")
+    }
 
     result.Model = &AlignofExprModel{Expr: d.Model}
     ret result
diff --git a/std/jule/sema/type.jule b/std/jule/sema/type.jule
index 165ab4e2e..0313b9c8a 100644
--- a/std/jule/sema/type.jule
+++ b/std/jule/sema/type.jule
@@ -1739,4 +1739,8 @@ fn applyImplicitCast(mut &dest: &TypeKind, mut &d: &Data) {
         applyCastKindModel(d, dest)
         ret
     }
+}
+
+fn validTypeForXof(mut &t: &TypeKind): bool {
+    ret !t.Void() && t.Fn() == nil
 }
\ No newline at end of file
diff --git a/std/mem/builtin.jule b/std/mem/builtin.jule
index f32489245..72775c9d6 100644
--- a/std/mem/builtin.jule
+++ b/std/mem/builtin.jule
@@ -4,11 +4,13 @@
 
 // Returns the size of the type in bytes.
 // If given expression, uses type of expression.
+// Void and function types are not supported.
 // fn SizeOf(TYPE || EXPRESSION): uint
 
 // Returns the alignment, in bytes, required for any instance of the type
 // indicated by type-id, which is either complete object type.
 // If given expression, uses type of expression.
+// Void and function types are not supported.
 // fn AlignOf(TYPE || EXPRESSION): uint
 
 // Frees memory.