diff --git a/base/runtime/virtual_memory_netbsd.odin b/base/runtime/virtual_memory_netbsd.odin
index 1e6ccbef9..bd24d2e19 100644
--- a/base/runtime/virtual_memory_netbsd.odin
+++ b/base/runtime/virtual_memory_netbsd.odin
@@ -6,7 +6,6 @@ import "base:intrinsics"
 VIRTUAL_MEMORY_SUPPORTED :: true
 
 SYS_munmap :: uintptr(73)
-SYS_mmap   :: uintptr(197)
 SYS_mremap :: uintptr(411)
 
 PROT_READ   :: 0x01
@@ -44,7 +43,7 @@ _get_superpage_size :: proc "contextless" () -> int {
 }
 
 _allocate_virtual_memory :: proc "contextless" (size: int) -> rawptr {
-	result, ok := intrinsics.syscall_bsd(SYS_mmap, 0, uintptr(size), PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, ~uintptr(0), 0)
+	result, ok := __netbsd_sys_mmap(nil, uint(size), PROT_READ|PROT_WRITE, i32(MAP_ANONYMOUS|MAP_PRIVATE), -1, 0, 0)
 	if !ok {
 		return nil
 	}
@@ -59,8 +58,11 @@ _allocate_virtual_memory_aligned :: proc "contextless" (size: int, alignment: in
 	// NOTE: Unlike FreeBSD, the NetBSD man pages do not indicate that
 	// `MAP_ALIGNED` can cause this to fail, so we don't try a second time with
 	// manual alignment.
-	map_aligned_n := intrinsics.count_trailing_zeros(uintptr(alignment)) << MAP_ALIGNMENT_SHIFT
-	result, ok := intrinsics.syscall_bsd(SYS_mmap, 0, uintptr(size), PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE|map_aligned_n, ~uintptr(0), 0)
+	map_aligned_n: u32
+	if alignment > page_size {
+		map_aligned_n = u32(intrinsics.count_trailing_zeros(uintptr(alignment)) << MAP_ALIGNMENT_SHIFT)
+	}
+	result, ok := __netbsd_sys_mmap(nil, uint(size), PROT_READ|PROT_WRITE, i32(MAP_ANONYMOUS|MAP_PRIVATE|map_aligned_n), -1, 0, 0)
 	if !ok {
 		return nil
 	}
@@ -72,19 +74,43 @@ _free_virtual_memory :: proc "contextless" (ptr: rawptr, size: int) {
 }
 
 _resize_virtual_memory :: proc "contextless" (ptr: rawptr, old_size: int, new_size: int, alignment: int) -> rawptr {
-	if alignment == 0 {
-		// The user does not care about alignment, which is the simpler case.
-		result, ok := intrinsics.syscall_bsd(SYS_mremap, uintptr(ptr), uintptr(old_size), uintptr(new_size), 0)
-		if !ok {
-			return nil
-		}
-		return rawptr(result)
-	} else {
-		map_aligned_n := intrinsics.count_trailing_zeros(uintptr(alignment)) << MAP_ALIGNMENT_SHIFT
-		result, ok := intrinsics.syscall_bsd(SYS_mremap, uintptr(ptr), uintptr(old_size), uintptr(new_size), map_aligned_n)
-		if !ok {
-			return nil
-		}
+	// NetBSD will not abide by `new_size` and `old_size` not being a multiple
+	// of the page size when remapping.
+	old_size_in_pages := old_size / page_size
+	if old_size % page_size != 0 {
+		old_size_in_pages += 1
+	}
+	new_size_in_pages := new_size / page_size
+	if new_size % page_size != 0 {
+		new_size_in_pages += 1
+	}
+	old_size_rounded := old_size_in_pages * page_size
+	new_size_rounded := new_size_in_pages * page_size
+
+	flags := uintptr(0)
+	if alignment > page_size {
+		flags = intrinsics.count_trailing_zeros(uintptr(alignment)) << MAP_ALIGNMENT_SHIFT
+	}
+
+	if result, ok := intrinsics.syscall_bsd(SYS_mremap, uintptr(ptr), uintptr(old_size_rounded), uintptr(new_size_rounded), 0, flags); ok {
 		return rawptr(result)
 	}
+
+	// It may not have been possible to extend the old address space.
+	// Try to allocate a new mapping and copy the old data.
+	new_ptr: rawptr
+	if alignment > page_size {
+		new_ptr = _allocate_virtual_memory_aligned(new_size, alignment)
+	} else {
+		new_ptr = _allocate_virtual_memory(new_size)
+	}
+
+	if new_ptr == nil {
+		// Memory allocation failed.
+		return nil
+	}
+
+	intrinsics.mem_copy_non_overlapping(new_ptr, ptr, min(old_size, new_size))
+	_free_virtual_memory(ptr, old_size)
+	return rawptr(new_ptr)
 }
diff --git a/base/runtime/virtual_memory_netbsd_amd64.asm b/base/runtime/virtual_memory_netbsd_amd64.asm
new file mode 100644
index 000000000..10b642f17
--- /dev/null
+++ b/base/runtime/virtual_memory_netbsd_amd64.asm
@@ -0,0 +1,36 @@
+bits 64
+
+%define SYS_mmap 197
+
+global __netbsd_sys_mmap
+
+; This is a workaround for NetBSD's standard mmap syscall needing seven
+; arguments (one of which is useless). The seventh must go on the stack,
+; and our syscall intrinsics do not currently handle stack-based arguments.
+section .text
+__netbsd_sys_mmap:
+	; These are the arguments for SYS_mmap.
+	;
+	; addr:  void*
+	; len:   size_t
+	; prot:  int
+	; flags: int
+	; fd:    int
+	; PAD:   long (unused)
+	; pos:   off_t
+
+	; Move the flags argument into the right register.
+	mov r10, rcx
+
+	mov rax, SYS_mmap
+	syscall
+
+	; Set the DL register to true if the Carry Flag is clear.
+	;
+	; This is where the 2nd return value will be taken from.
+	;
+	; This is valid for the System V AMD64 ABI, as 128-bit return
+	; values may be stored in RAX:RDX.
+	setnb dl
+
+	ret
diff --git a/base/runtime/virtual_memory_netbsd_amd64.odin b/base/runtime/virtual_memory_netbsd_amd64.odin
new file mode 100644
index 000000000..ac6526d98
--- /dev/null
+++ b/base/runtime/virtual_memory_netbsd_amd64.odin
@@ -0,0 +1,13 @@
+#+private
+package runtime
+
+import "base:intrinsics"
+
+foreign import netbsd_asm "virtual_memory_netbsd_amd64.asm"
+
+@(private="file")
+c_long :: i32 when size_of(rawptr) == 4 else i64
+
+foreign netbsd_asm {
+	__netbsd_sys_mmap :: proc "c" (addr: rawptr, len: uint, prot: i32, flags: i32, fd: i32, PAD: c_long, pos: i64) -> (rawptr, bool) ---
+}
diff --git a/base/runtime/virtual_memory_netbsd_arm64.asm b/base/runtime/virtual_memory_netbsd_arm64.asm
new file mode 100644
index 000000000..24ed4a997
--- /dev/null
+++ b/base/runtime/virtual_memory_netbsd_arm64.asm
@@ -0,0 +1,23 @@
+.set SYS_mmap, 197
+
+.global __netbsd_sys_mmap
+
+// This is a workaround for NetBSD's standard mmap syscall needing seven
+// arguments (one of which is useless). The seventh must go on the stack,
+// and our syscall intrinsics do not currently handle stack-based arguments.
+.section .text
+__netbsd_sys_mmap:
+	// These are the arguments for SYS_mmap.
+	//
+	// addr:  void*
+	// len:   size_t
+	// prot:  int
+	// flags: int
+	// fd:    int
+	// PAD:   long (unused)
+	// pos:   off_t
+
+	mov x17, SYS_mmap
+	svc #0
+
+	cset x1, cc
diff --git a/base/runtime/virtual_memory_netbsd_arm64.odin b/base/runtime/virtual_memory_netbsd_arm64.odin
new file mode 100644
index 000000000..02fce151a
--- /dev/null
+++ b/base/runtime/virtual_memory_netbsd_arm64.odin
@@ -0,0 +1,13 @@
+#+private
+package runtime
+
+import "base:intrinsics"
+
+foreign import netbsd_asm "virtual_memory_netbsd_arm64.asm"
+
+@(private="file")
+c_long :: i32 when size_of(rawptr) == 4 else i64
+
+foreign netbsd_asm {
+	__netbsd_sys_mmap :: proc "c" (addr: rawptr, len: uint, prot: i32, flags: i32, fd: i32, PAD: c_long, pos: i64) -> (rawptr, bool) ---
+}