diff --git a/include/sigar.h b/include/sigar.h
index fdd732bf..7babe5c9 100644
--- a/include/sigar.h
+++ b/include/sigar.h
@@ -134,7 +134,9 @@ typedef struct {
     sigar_uint64_t
         total,
         used, 
-        free;
+        free,
+        page_in,
+        page_out;
 } sigar_swap_t;
 
 SIGAR_DECLARE(int) sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap);
diff --git a/src/os/aix/aix_sigar.c b/src/os/aix/aix_sigar.c
index 2ff8a9ef..a2c3ec53 100644
--- a/src/os/aix/aix_sigar.c
+++ b/src/os/aix/aix_sigar.c
@@ -684,6 +684,8 @@ static int sigar_swap_get_perfstat(sigar_t *sigar, sigar_swap_t *swap)
 
 int sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap)
 {
+    swap->page_in = swap->page_out = -1;
+
     if (sigar_perfstat_init(sigar) == SIGAR_OK) {
         sigar_log(sigar, SIGAR_LOG_DEBUG, "[swap] using libperfstat");
         return sigar_swap_get_perfstat(sigar, swap);
diff --git a/src/os/darwin/darwin_sigar.c b/src/os/darwin/darwin_sigar.c
index e8c48bac..7a98c005 100644
--- a/src/os/darwin/darwin_sigar.c
+++ b/src/os/darwin/darwin_sigar.c
@@ -450,6 +450,7 @@ int sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap)
 
     swap->free = swap->total - swap->used;
 
+    swap->page_in = swap->page_out = -1;
 #elif defined(__FreeBSD__)
     struct kvm_swap kswap[1];
 
@@ -473,6 +474,8 @@ int sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap)
     swap->total = kswap[0].ksw_total * sigar->pagesize;
     swap->used  = kswap[0].ksw_used * sigar->pagesize;
     swap->free  = swap->total - swap->used;
+
+    swap->page_in = swap->page_out = -1;
 #else
     /*XXX OpenBSD*/
 #endif
diff --git a/src/os/hpux/hpux_sigar.c b/src/os/hpux/hpux_sigar.c
index 2ddab16c..6fd44e75 100644
--- a/src/os/hpux/hpux_sigar.c
+++ b/src/os/hpux/hpux_sigar.c
@@ -116,7 +116,9 @@ int sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap)
     }
 
     swap->used = swap->total - swap->free;
-    
+
+    swap->page_in = swap->page_out = -1;    
+
     return SIGAR_OK;
 }
 
diff --git a/src/os/linux/linux_sigar.c b/src/os/linux/linux_sigar.c
index 413aa8d1..467a2c3e 100644
--- a/src/os/linux/linux_sigar.c
+++ b/src/os/linux/linux_sigar.c
@@ -438,6 +438,8 @@ int sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap)
     swap->free   = sigar_meminfo(buffer, MEMINFO_PARAM("SwapFree"));
     swap->used   = swap->total - swap->free;
 
+    swap->page_in = swap->page_out = -1;
+
     return SIGAR_OK;
 }
 
diff --git a/src/os/netware/netware_sigar.c b/src/os/netware/netware_sigar.c
index 48a2978c..bfbb3de2 100644
--- a/src/os/netware/netware_sigar.c
+++ b/src/os/netware/netware_sigar.c
@@ -130,6 +130,7 @@ int sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap)
     swap->used  = info.SwapPageCount * PAGESIZE;
     swap->free  = info.SwapFreeCount * PAGESIZE;
     swap->total = swap->used + swap->free;
+    swap->page_in = swap->page_out = -1;
 
     return SIGAR_OK;
 }
diff --git a/src/os/osf1/osf1_sigar.c b/src/os/osf1/osf1_sigar.c
index f124f14a..9dcfc641 100644
--- a/src/os/osf1/osf1_sigar.c
+++ b/src/os/osf1/osf1_sigar.c
@@ -86,6 +86,8 @@ int sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap)
 
     swap->used   = swap->total - swap->free;
 
+    swap->page_in = swap->page_out = -1;
+
     return SIGAR_OK;
 }
 
diff --git a/src/os/solaris/solaris_sigar.c b/src/os/solaris/solaris_sigar.c
index 9c576d3f..0ebeda6f 100644
--- a/src/os/solaris/solaris_sigar.c
+++ b/src/os/solaris/solaris_sigar.c
@@ -246,6 +246,8 @@ int sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap)
     swap->free  <<= sigar->pagesize;
     swap->used  <<= sigar->pagesize;
 
+    swap->page_in = swap->page_out = -1;
+
     return SIGAR_OK;
 }
 
diff --git a/src/os/stub/stub_sigar.c b/src/os/stub/stub_sigar.c
index d45262f0..e9bfeaf2 100644
--- a/src/os/stub/stub_sigar.c
+++ b/src/os/stub/stub_sigar.c
@@ -37,6 +37,8 @@ int sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap)
     swap->total  = -1;
     swap->used   = -1;
     swap->free   = -1;
+    swap->page_in = -1;
+    swap->page_out = -1;
 
     return SIGAR_OK;
 }
diff --git a/src/os/win32/win32_sigar.c b/src/os/win32/win32_sigar.c
index 7a58f7ea..23bb5e65 100644
--- a/src/os/win32/win32_sigar.c
+++ b/src/os/win32/win32_sigar.c
@@ -545,6 +545,8 @@ SIGAR_DECLARE(int) sigar_swap_get(sigar_t *sigar, sigar_swap_t *swap)
 
     swap->used = swap->total - swap->free;
 
+    swap->page_in = swap->page_out = -1;
+
     return SIGAR_OK;
 }