diff --git a/src/constants.F90 b/src/constants.F90
index e9999c0bdd..564e0baedd 100644
--- a/src/constants.F90
+++ b/src/constants.F90
@@ -20,7 +20,7 @@ module constants
        FILETYPE_PARTICLE_RESTART = -2
 
   ! ============================================================================
-  ! ADJUSTABLE PARAMETERS 
+  ! ADJUSTABLE PARAMETERS
 
   ! NOTE: This is the only section of the constants module that should ever be
   ! adjusted. Modifying constants in other sections may cause the code to fail.
@@ -50,6 +50,10 @@ module constants
   integer, parameter :: MAX_WORD_LEN = 150
   integer, parameter :: MAX_FILE_LEN = 255
 
+  ! Maximum number of external source spatial resamples to encounter before an
+  ! error is thrown.
+  integer, parameter :: MAX_EXTSRC_RESAMPLES = 10000
+
   ! ============================================================================
   ! PHYSICAL CONSTANTS
 
@@ -110,9 +114,9 @@ module constants
 
   ! Surface types
   integer, parameter ::  &
-       SURF_PX     =  1, & ! Plane parallel to x-plane 
-       SURF_PY     =  2, & ! Plane parallel to y-plane 
-       SURF_PZ     =  3, & ! Plane parallel to z-plane 
+       SURF_PX     =  1, & ! Plane parallel to x-plane
+       SURF_PY     =  2, & ! Plane parallel to y-plane
+       SURF_PZ     =  3, & ! Plane parallel to z-plane
        SURF_PLANE  =  4, & ! Arbitrary plane
        SURF_CYL_X  =  5, & ! Cylinder along x-axis
        SURF_CYL_Y  =  6, & ! Cylinder along y-axis
@@ -143,7 +147,7 @@ module constants
        ELECTRON = 3
 
   ! Angular distribution type
-  integer, parameter :: & 
+  integer, parameter :: &
        ANGLE_ISOTROPIC = 1, & ! Isotropic angular distribution
        ANGLE_32_EQUI   = 2, & ! 32 equiprobable bins
        ANGLE_TABULAR   = 3    ! Tabular angular distribution
@@ -275,7 +279,7 @@ module constants
        SCORE_KAPPA_FISSION = -12, & ! fission energy production rate
        SCORE_CURRENT       = -13, & ! partial current
        SCORE_EVENTS        = -14    ! number of events
-       
+
   ! Maximum scattering order supported
   integer, parameter :: SCATT_ORDER_MAX = 10
   character(len=*), parameter :: SCATT_ORDER_MAX_PNSTR = "scatter-p10"
@@ -322,7 +326,7 @@ module constants
 
   ! Source angular distribution types
   integer, parameter :: &
-       SRC_ANGLE_ISOTROPIC = 1, & ! Isotropic angular 
+       SRC_ANGLE_ISOTROPIC = 1, & ! Isotropic angular
        SRC_ANGLE_MONO      = 2, & ! Monodirectional source
        SRC_ANGLE_TABULAR   = 3    ! Tabular distribution
 
@@ -332,7 +336,7 @@ module constants
        SRC_ENERGY_MAXWELL = 2, & ! Maxwell fission spectrum
        SRC_ENERGY_WATT    = 3, & ! Watt fission spectrum
        SRC_ENERGY_TABULAR = 4    ! Tabular distribution
-       
+
   ! ============================================================================
   ! MISCELLANEOUS CONSTANTS
 
diff --git a/src/source.F90 b/src/source.F90
index 57870206de..4fcdd0074a 100644
--- a/src/source.F90
+++ b/src/source.F90
@@ -76,6 +76,7 @@ contains
     real(8) :: b          ! Arbitrary parameter 'b'
     logical :: found      ! Does the source particle exist within geometry?
     type(Particle) :: p   ! Temporary particle for using find_cell
+    integer, save :: num_resamples = 0 ! Number of resamples encountered
 
     ! Set weight to one by default
     site % wgt = ONE
@@ -99,7 +100,14 @@ contains
 
         ! Now search to see if location exists in geometry
         call find_cell(p, found)
-
+        if (.not. found) then
+          num_resamples = num_resamples + 1
+          if (num_resamples == MAX_EXTSRC_RESAMPLES) then
+            message = "Maximum number of external source spatial resamples &
+                      &reached!"
+            call fatal_error()
+          end if
+        end if
       end do
 
     case (SRC_SPACE_POINT)