diff --git a/doc/classes/Decal.xml b/doc/classes/Decal.xml
index b63f6e72528..75974664a77 100644
--- a/doc/classes/Decal.xml
+++ b/doc/classes/Decal.xml
@@ -87,7 +87,8 @@
 			[b]Note:[/b] Setting [member normal_fade] to a value greater than [code]0.0[/code] has a small performance cost due to the added normal angle computations.
 		</member>
 		<member name="size" type="Vector3" setter="set_size" getter="get_size" default="Vector3(2, 2, 2)">
-			Sets the size of the [AABB] used by the decal. The AABB goes from [code]-size/2[/code] to [code]size/2[/code].
+			Sets the size of the [AABB] used by the decal. All dimensions must be set to a value greater than zero (they will be clamped to [code]0.001[/code] if this is not the case). The AABB goes from [code]-size/2[/code] to [code]size/2[/code].
+			[b]Note:[/b] To improve culling efficiency of "hard surface" decals, set their [member upper_fade] and [member lower_fade] to [code]0.0[/code] and set the Y component of the [member size] as low as possible. This will reduce the decals' AABB size without affecting their appearance.
 		</member>
 		<member name="texture_albedo" type="Texture2D" setter="set_texture" getter="get_texture">
 			[Texture2D] with the base [Color] of the Decal. Either this or the [member texture_emission] must be set for the Decal to be visible. Use the alpha channel like a mask to smoothly blend the edges of the decal with the underlying object.
diff --git a/scene/3d/decal.cpp b/scene/3d/decal.cpp
index e122adcc8c4..6f2717fd417 100644
--- a/scene/3d/decal.cpp
+++ b/scene/3d/decal.cpp
@@ -31,7 +31,7 @@
 #include "decal.h"
 
 void Decal::set_size(const Vector3 &p_size) {
-	size = p_size;
+	size = Vector3(MAX(0.001, p_size.x), MAX(0.001, p_size.y), MAX(0.001, p_size.z));
 	RS::get_singleton()->decal_set_size(decal, p_size);
 	update_gizmos();
 }