diff --git a/src/Expr.cc b/src/Expr.cc
index cb932ff7ee..be186524ad 100644
--- a/src/Expr.cc
+++ b/src/Expr.cc
@@ -1795,7 +1795,20 @@ Val* DivideExpr::AddrFold(Val* v1, Val* v2) const
 	else
 		mask = static_cast<uint32>(v2->InternalInt());
 
-	return new SubNetVal(v1->AsAddr(), mask);
+	auto& a = v1->AsAddr();
+
+	if ( a.GetFamily() == IPv4 )
+		{
+		if ( mask > 32 )
+			RuntimeError(fmt("bad IPv4 subnet prefix length: %" PRIu32, mask));
+		}
+	else
+		{
+		if ( mask > 128 )
+			RuntimeError(fmt("bad IPv6 subnet prefix length: %" PRIu32, mask));
+		}
+
+	return new SubNetVal(a, mask);
 	}
 
 IMPLEMENT_SERIAL(DivideExpr, SER_DIVIDE_EXPR);
diff --git a/src/IPAddr.cc b/src/IPAddr.cc
index 7ccc3dce07..7917e82c29 100644
--- a/src/IPAddr.cc
+++ b/src/IPAddr.cc
@@ -216,7 +216,10 @@ IPPrefix::IPPrefix(const in4_addr& in4, uint8_t length)
 	: prefix(in4), length(96 + length)
 	{
 	if ( length > 32 )
-		reporter->InternalError("Bad in4_addr IPPrefix length : %d", length);
+		{
+		reporter->Error("Bad in4_addr IPPrefix length : %d", length);
+		this->length = 0;
+		}
 
 	prefix.Mask(this->length);
 	}
@@ -225,7 +228,10 @@ IPPrefix::IPPrefix(const in6_addr& in6, uint8_t length)
 	: prefix(in6), length(length)
 	{
 	if ( length > 128 )
-		reporter->InternalError("Bad in6_addr IPPrefix length : %d", length);
+		{
+		reporter->Error("Bad in6_addr IPPrefix length : %d", length);
+		this->length = 0;
+		}
 
 	prefix.Mask(this->length);
 	}
@@ -236,19 +242,23 @@ IPPrefix::IPPrefix(const IPAddr& addr, uint8_t length, bool len_is_v6_relative)
 	if ( prefix.GetFamily() == IPv4 && ! len_is_v6_relative )
 		{
 		if ( length > 32 )
-			reporter->InternalError("Bad IPAddr(v4) IPPrefix length : %d",
-			                        length);
-
-		this->length = length + 96;
+			{
+			reporter->Error("Bad IPAddr(v4) IPPrefix length : %d", length);
+			this->length = 0;
+			}
+		else
+			this->length = length + 96;
 		}
 
 	else
 		{
 		if ( length > 128 )
-			reporter->InternalError("Bad IPAddr(v6) IPPrefix length : %d",
-			                        length);
-
-		this->length = length;
+			{
+			reporter->Error("Bad IPAddr(v6) IPPrefix length : %d", length);
+			this->length = 0;
+			}
+		else
+			this->length = length;
 		}
 
 	prefix.Mask(this->length);
diff --git a/testing/btest/Baseline/language.subnet-errors/out b/testing/btest/Baseline/language.subnet-errors/out
new file mode 100644
index 0000000000..5d8e3d76da
--- /dev/null
+++ b/testing/btest/Baseline/language.subnet-errors/out
@@ -0,0 +1,5 @@
+expression error in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.subnet-errors/subnet-errors.bro, line 9: bad IPv4 subnet prefix length: 33 (1.2.3.4 / i)
+expression error in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.subnet-errors/subnet-errors.bro, line 18: bad IPv6 subnet prefix length: 129 (:: / i)
+1.2.3.4/32
+::/128
+init last
diff --git a/testing/btest/language/subnet-errors.bro b/testing/btest/language/subnet-errors.bro
new file mode 100644
index 0000000000..fa98dcec48
--- /dev/null
+++ b/testing/btest/language/subnet-errors.bro
@@ -0,0 +1,26 @@
+# @TEST-EXEC: bro -b %INPUT >out 2>&1
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff out
+
+event bro_init()
+	{
+	local i = 32;
+	print 1.2.3.4/i;
+	++i;
+	print 1.2.3.4/i;
+	print "init 1";
+	}
+
+event bro_init()
+	{
+	local i = 128;
+	print [::]/i;
+	++i;
+	print [::]/i;
+	print "init 1";
+	}
+
+event bro_init() &priority=-10
+	{
+	print "init last";
+	}
+