diff --git a/js/src/vm/ArrayBufferObject.cpp b/js/src/vm/ArrayBufferObject.cpp
index e43edab690..da51abec63 100644
--- a/js/src/vm/ArrayBufferObject.cpp
+++ b/js/src/vm/ArrayBufferObject.cpp
@@ -943,7 +943,9 @@ ArrayBufferObject::wasmGrowToSizeInPlace(uint32_t newSize,
     // wasm-visible length of the buffer has been increased so it must be the
     // last fallible operation.
 
-    // byteLength can be at most INT32_MAX.
+    // byteLength can be at most INT32_MAX. Note: if this hard limit changes,
+    // update the clamping behavior in wasm::DecodeMemoryLimits and remove this
+    // comment as well as the one in wasmMovingGrowToSize.
     if (newSize > INT32_MAX)
         return false;
 
@@ -974,6 +976,7 @@ ArrayBufferObject::wasmMovingGrowToSize(uint32_t newSize,
     // unmodified and valid.
 
     // byteLength can be at most INT32_MAX.
+    // See comment in wasmGrowToSizeInPlace about wasm::DecodeMemoryLimits.
     if (newSize > INT32_MAX)
         return false;
 
diff --git a/js/src/wasm/WasmBinaryConstants.h b/js/src/wasm/WasmBinaryConstants.h
index 3c8c49058c..616a9b05e8 100644
--- a/js/src/wasm/WasmBinaryConstants.h
+++ b/js/src/wasm/WasmBinaryConstants.h
@@ -363,7 +363,8 @@ static const unsigned MaxStringBytes         =   100000;
 static const unsigned MaxLocals              =    50000;
 static const unsigned MaxParams              =     1000;
 static const unsigned MaxBrTableElems        =  1000000;
-static const unsigned MaxMemoryInitialBytes  = 1024 * 1024 * 1024;
+static const unsigned MaxMemoryInitialPages  = 16384;
+static const unsigned MaxMemoryMaximumPages  = 65536;
 static const unsigned MaxModuleBytes         = 1024 * 1024 * 1024;
 static const unsigned MaxFunctionBytes       =         128 * 1024;
 
diff --git a/js/src/wasm/WasmValidate.cpp b/js/src/wasm/WasmValidate.cpp
index 6617ff9ff8..0904b741c2 100644
--- a/js/src/wasm/WasmValidate.cpp
+++ b/js/src/wasm/WasmValidate.cpp
@@ -917,20 +917,23 @@ DecodeMemoryLimits(Decoder& d, ModuleEnvironment* env)
     if (!DecodeLimits(d, &memory))
         return false;
 
+    if (memory.initial > MaxMemoryInitialPages)
+        return d.fail("initial memory size too big");
     CheckedInt<uint32_t> initialBytes = memory.initial;
     initialBytes *= PageSize;
-    if (!initialBytes.isValid() || initialBytes.value() > MaxMemoryInitialBytes)
-        return d.fail("initial memory size too big");
+    MOZ_ASSERT(initialBytes.isValid());
 
     memory.initial = initialBytes.value();
 
     if (memory.maximum) {
+       if (*memory.maximum > MaxMemoryMaximumPages)
+            return d.fail("maximum memory size too big");
         CheckedInt<uint32_t> maximumBytes = *memory.maximum;
         maximumBytes *= PageSize;
-        if (!maximumBytes.isValid())
-            return d.fail("maximum memory size too big");
 
-        memory.maximum = Some(maximumBytes.value());
+        // Clamp the maximum memory value to UINT32_MAX; it's not semantically
+        // visible since growing will fail for values greater than INT32_MAX.
+        memory.maximum = Some(maximumBytes.isValid() ? maximumBytes.value() : UINT32_MAX);
     }
 
     env->memoryUsage = MemoryUsage::Unshared;
@@ -1547,7 +1550,7 @@ DecodeDataSection(Decoder& d, ModuleEnvironment* env)
         if (!d.readVarU32(&seg.length))
             return d.fail("expected segment size");
 
-        if (seg.length > MaxMemoryInitialBytes)
+        if (seg.length > MaxMemoryInitialPages * PageSize)
             return d.fail("segment size too big");
         seg.bytecodeOffset = d.currentOffset();