diff --git a/bootstrap/unix-44/Heap.c b/bootstrap/unix-44/Heap.c
index 1afb3591..e1dac3b3 100644
--- a/bootstrap/unix-44/Heap.c
+++ b/bootstrap/unix-44/Heap.c
@@ -290,7 +290,7 @@ SYSTEM_PTR Heap_NEWREC (INT32 tag)
 				if (Heap_firstTry) {
 					Heap_GC(1);
 					blksz += 16;
-					t = __LSHR(Heap_allocated + blksz, 2, 32) * 5;
+					t = __LSH(Heap_allocated + blksz, -(Heap_ldUnit + 2), 32) * 80;
 					if (Heap_uLT(Heap_heapsize, t)) {
 						Heap_ExtendHeap(t - Heap_heapsize);
 					}
diff --git a/bootstrap/unix-48/Heap.c b/bootstrap/unix-48/Heap.c
index 1afb3591..e1dac3b3 100644
--- a/bootstrap/unix-48/Heap.c
+++ b/bootstrap/unix-48/Heap.c
@@ -290,7 +290,7 @@ SYSTEM_PTR Heap_NEWREC (INT32 tag)
 				if (Heap_firstTry) {
 					Heap_GC(1);
 					blksz += 16;
-					t = __LSHR(Heap_allocated + blksz, 2, 32) * 5;
+					t = __LSH(Heap_allocated + blksz, -(Heap_ldUnit + 2), 32) * 80;
 					if (Heap_uLT(Heap_heapsize, t)) {
 						Heap_ExtendHeap(t - Heap_heapsize);
 					}
diff --git a/bootstrap/unix-88/Heap.c b/bootstrap/unix-88/Heap.c
index 2951a621..bc1ace8e 100644
--- a/bootstrap/unix-88/Heap.c
+++ b/bootstrap/unix-88/Heap.c
@@ -290,7 +290,7 @@ SYSTEM_PTR Heap_NEWREC (INT64 tag)
 				if (Heap_firstTry) {
 					Heap_GC(1);
 					blksz += 32;
-					t = __LSHR(Heap_allocated + blksz, 2, 64) * 5;
+					t = __LSH(Heap_allocated + blksz, -(Heap_ldUnit + 2), 64) * 160;
 					if (Heap_uLT(Heap_heapsize, t)) {
 						Heap_ExtendHeap(t - Heap_heapsize);
 					}
diff --git a/bootstrap/windows-48/Heap.c b/bootstrap/windows-48/Heap.c
index 1afb3591..e1dac3b3 100644
--- a/bootstrap/windows-48/Heap.c
+++ b/bootstrap/windows-48/Heap.c
@@ -290,7 +290,7 @@ SYSTEM_PTR Heap_NEWREC (INT32 tag)
 				if (Heap_firstTry) {
 					Heap_GC(1);
 					blksz += 16;
-					t = __LSHR(Heap_allocated + blksz, 2, 32) * 5;
+					t = __LSH(Heap_allocated + blksz, -(Heap_ldUnit + 2), 32) * 80;
 					if (Heap_uLT(Heap_heapsize, t)) {
 						Heap_ExtendHeap(t - Heap_heapsize);
 					}
diff --git a/bootstrap/windows-88/Heap.c b/bootstrap/windows-88/Heap.c
index 2951a621..bc1ace8e 100644
--- a/bootstrap/windows-88/Heap.c
+++ b/bootstrap/windows-88/Heap.c
@@ -290,7 +290,7 @@ SYSTEM_PTR Heap_NEWREC (INT64 tag)
 				if (Heap_firstTry) {
 					Heap_GC(1);
 					blksz += 32;
-					t = __LSHR(Heap_allocated + blksz, 2, 64) * 5;
+					t = __LSH(Heap_allocated + blksz, -(Heap_ldUnit + 2), 64) * 160;
 					if (Heap_uLT(Heap_heapsize, t)) {
 						Heap_ExtendHeap(t - Heap_heapsize);
 					}