diff --git a/src/main/java/org/apposed/appose/shm/ShmBase.java b/src/main/java/org/apposed/appose/shm/ShmBase.java
index 83b6349..e3191da 100644
--- a/src/main/java/org/apposed/appose/shm/ShmBase.java
+++ b/src/main/java/org/apposed/appose/shm/ShmBase.java
@@ -116,6 +116,9 @@ protected static class ShmInfo<HANDLE> {
 		/** Size in bytes. */
 		int size;
 
+		/** Size in bytes allocated by the operating system. */
+		int totalSize;
+
 		/** Pointer referencing the shared memory. */
 		Pointer pointer;
 
diff --git a/src/main/java/org/apposed/appose/shm/ShmLinux.java b/src/main/java/org/apposed/appose/shm/ShmLinux.java
index ac5e06f..9c35c6b 100644
--- a/src/main/java/org/apposed/appose/shm/ShmLinux.java
+++ b/src/main/java/org/apposed/appose/shm/ShmLinux.java
@@ -119,7 +119,8 @@ private static ShmInfo<Integer> prepareShm(String name, boolean create, int size
 			}
 
 			ShmInfo<Integer> info = new ShmInfo<>();
-			info.size = shm_size;
+			info.size = size;
+			info.totalSize = shm_size;
 			info.name = withoutLeadingSlash(shm_name);
 			info.pointer = pointer;
 			info.handle = shmFd;
diff --git a/src/main/java/org/apposed/appose/shm/ShmMacOS.java b/src/main/java/org/apposed/appose/shm/ShmMacOS.java
index 388a2cc..2afeb87 100644
--- a/src/main/java/org/apposed/appose/shm/ShmMacOS.java
+++ b/src/main/java/org/apposed/appose/shm/ShmMacOS.java
@@ -110,7 +110,8 @@ private static ShmInfo<Integer> prepareShm(String name, boolean create, int size
 			}
 
 			ShmInfo<Integer> info = new ShmInfo<>();
-			info.size = shm_size;
+			info.size = size;
+			info.totalSize = shm_size;
 			info.name = withoutLeadingSlash(shm_name);
 			info.pointer = pointer;
 			info.handle = shmFd;
diff --git a/src/main/java/org/apposed/appose/shm/ShmWindows.java b/src/main/java/org/apposed/appose/shm/ShmWindows.java
index c558d4a..8cfbbc3 100644
--- a/src/main/java/org/apposed/appose/shm/ShmWindows.java
+++ b/src/main/java/org/apposed/appose/shm/ShmWindows.java
@@ -122,7 +122,8 @@ private static ShmInfo<WinNT.HANDLE> prepareShm(String name, boolean create, int
 			}
 
 			ShmInfo<WinNT.HANDLE> info = new ShmInfo<>();
-			info.size = shm_size;
+			info.size = size;
+			info.totalSize = shm_size;
 			info.name = shm_name;
 			info.pointer = pointer;
 			info.writePointer = writePointer;